Here is a list of all namespaces with brief descriptions:

[detail level 12345]

_Detail
Alembic	Alembic namespace ..
Abc
ALEMBIC_VERSION_NS
AbcCollection
ALEMBIC_VERSION_NS
AbcCoreAbstract
ALEMBIC_VERSION_NS
IllustrationOnly
AbcCoreFactory
ALEMBIC_VERSION_NS
AbcCoreHDF5
ALEMBIC_VERSION_NS
AbcCoreLayer
ALEMBIC_VERSION_NS
AbcCoreOgawa
ALEMBIC_VERSION_NS
AbcGeom
ALEMBIC_VERSION_NS
AbcMaterial
ALEMBIC_VERSION_NS
Util
ALEMBIC_VERSION_NS
bjhash
BRAY
cl	The OpenCL C++ bindings are defined within this namespace
detail
CubeMap
cv
EXPR
farmhash
fasthash
FBX_Names
Filesystem	Platform-independent utilities for manipulating file names, files, directories, and other file system miscellany
FMT_BEGIN_NAMESPACE
fpu
GA_FileFormatH9
GA_HandleDetail
GA_Homogenize	Homogenize/dehomogenize that only operate on UT_Vector4
GA_Names
GA_PageArrayIO
GA_PrimCompat
GA_Private
GABC_NAMESPACE
GABC_GTUtil
GD_PrimTypeCompat
GEO
geo_hedge
GEO_PrimTypeCompat
GQ_PolyDelaunayImpl
GQ_StraightSkeletonImpl
GR_ShapeFactory
GR_Utils	Utility GR methods common to all renderers
GT_DeformUtils
GT_GUHelpers
GT_Names
GT_PointSplat
GU
GU_AgentBlendShapeUtils
GU_Blend
GU_Classify
GU_CleanTools
GU_Copy
NeededTransforms
GU_CurveFrame
GU_Decomposition
GU_ExtractTransform
GU_Flatten2
GU_LocalFrame
GU_LocalTransform
GU_PackedFactoryPrivate
GU_PolyBevel3
GU_PolyFill
GU_PolyReduce2
GU_Remesh
GU_ShrinkTools
GU_Snap
GU_UVFlatten
GU_UVUtils
GU_VDBPointToolsInternal
GusdUSD_StdTraverse
GusdUSD_ThreadedTraverse
GusdUSD_Utils
hboost
python
HDK_Sample	This namespace is used to hold all HDK example source code
GU_Copy
NeededTransforms
GU_CurveFrame
UT
HOIIO_v2_0
HUSD_BRAY_NS
IEX_INTERNAL_NAMESPACE
IEX_NAMESPACE
ILMTHREAD_INTERNAL_NAMESPACE
ILMTHREAD_NAMESPACE
ImageBufAlgo
IMATH_INTERNAL_NAMESPACE
IMATH_NAMESPACE
internal
LatLongMap
murmur
OP_Utils
OPENEXR_IMF_INTERNAL_NAMESPACE
OPENEXR_IMF_NAMESPACE
openvdb
OPENVDB_VERSION_NAME
compression
internal
io
logging
math
internal
mat3_internal
pcg
internal
points
attribute_traits
future
index
index_filter_internal
internal
point_advect_internal
point_attribute_internal
point_conversion_internal
point_delete_internal
point_group_internal
point_mask_internal
point_move_internal
point_sample_internal
point_scatter_internal
tools
activation
clip_internal
composite
diagnostics_internal
ds
filter_internal
gridop
internal
level_set_fracture_internal
level_set_util_internal
local_util
lstrack
mask_internal
mesh_to_volume_internal
p2ls_internal
particle_atlas_internal
point_index_grid_internal
point_partitioner_internal
poisson
internal
potential_flow_internal
Scheme
stats_internal
ttls_internal
v2s_internal
valxform
volume_to_mesh_internal
tree
internal
iter
leafmgr
util
PI_PythonState
Plugin
pss
internal
pugi
pvt
pxr_half
PXR_INTERNAL_NS
PXR_NS
RgbaYca
Sdf_PySpecDetail
ShaderMetadataHelpers
SIM
FieldUtils
SIM_ConstraintNetwork
simd
SOP_AddEnums
SOP_AgentUnpackEnums
SOP_AttribCreate_2_0Enums
SOP_AttribFromVolumeEnums
SOP_AttribInterpolateEnums
SOP_AttribMirrorEnums
SOP_AttribPromoteEnums
SOP_AttribSwapEnums
SOP_BlastEnums
SOP_BlendShapes_2_0Enums
SOP_BoneCaptureBiharmonicEnums
SOP_BoneCaptureLinesEnums
SOP_BoneDeformEnums
SOP_BooleanEnums
SOP_BoundEnums
SOP_CaptureAttribPackEnums
SOP_CaptureAttribUnpackEnums
SOP_CircleEnums
SOP_CircleFromEdgesEnums
SOP_ClipEnums
SOP_ConnectivityEnums
SOP_ControlEnums
SOP_ConvertEnums
SOP_ConvexDecompositionEnums
SOP_CopyToPoints_2_0Enums
SOP_CopyToPointsEnums
SOP_CopyTransformEnums
SOP_CurveEnums
SOP_CurveFrameEnums
SOP_CurveNetworkEnums
SOP_DeleteEnums
SOP_Dissolve_2_0Enums
SOP_EdgeEqualizeEnums
SOP_EdgeStraightenEnums
SOP_EdgeTransportEnums
SOP_EndsEnums
SOP_EnumerateEnums
SOP_ErrorNodeEnums
SOP_ExtractCentroidEnums
SOP_ExtractTransformEnums
SOP_FacetEnums
SOP_FileEnums
SOP_Fuse_2_0Enums
SOP_FuseEnums
SOP_GridEnums
SOP_GroupCombineEnums
SOP_GroupCreateEnums
SOP_GroupDeleteEnums
SOP_GroupExpandEnums
SOP_GroupFindPathEnums
SOP_GroupPromoteEnums
SOP_GroupRangeEnums
SOP_GroupRenameEnums
SOP_GuideMaskEnums
SOP_GuideProcessCoreEnums
SOP_HairClumpEnums
SOP_HairGenCoreEnums
SOP_InvokeEnums
SOP_JoinEnums
SOP_KnifeEnums
SOP_LineEnums
SOP_Measure_2_0Enums
SOP_MeasureEnums
SOP_NameEnums
SOP_NormalEnums
SOP_OpenCLEnums
SOP_PeakEnums
SOP_PolyBevel_3_0Enums
SOP_PolyCutEnums
SOP_PolyDoctorEnums
SOP_PolyExpand2DEnums
SOP_PolyFillEnums
SOP_PolyFrameEnums
SOP_PolyReduce_2_0Enums
SOP_PrimitiveEnums
SOP_ProximityCaptureEnums
SOP_RayEnums
SOP_Remesh_2_0Enums
SOP_ResampleEnums
SOP_RestEnums
SOP_ReverseEnums
SOP_RevolveEnums
SOP_RewireEnums
SOP_SBlend_2_0Enums
SOP_Scatter_2_0Enums
SOP_ShapeDiffEnums
SOP_Smooth_2_0Enums
SOP_SortEnums
SOP_SphereEnums
SOP_SplitPointsEnums
SOP_Sweep_2_0Enums
SOP_SwitchIfEnums
SOP_Tetrahedralize_2_0Enums
SOP_TorusEnums
SOP_TransformAxisEnums
SOP_TransformByAttribEnums
SOP_TransformEnums
SOP_Triangulate2D_2_0Enums
SOP_Triangulate2D_3_0Enums
SOP_TubeEnums
SOP_UVAutoseamEnums
SOP_UVFlatten_2_0Enums
SOP_UVFlatten_3_0Enums
sop_uvflatten_private
SOP_UVLayout_2_0Enums
SOP_UVLayout_3_0Enums
sop_uvlayout_private
sop_uvpelt2_private
SOP_UVProjectEnums
SOP_UVTransform_2_0Enums
SOP_UVUnwrapEnums
SOP_VolumeAnalysisEnums
SOP_VolumeBinEnums
SOP_VolumeBlurEnums
SOP_VolumeBoundEnums
SOP_VolumeBreakEnums
SOP_VolumeCompressEnums
SOP_VolumeConvolve3Enums
SOP_VolumeFFTEnums
SOP_VolumeFromAttribEnums
SOP_VolumeMergeEnums
SOP_VolumeMixEnums
SOP_VolumeRasterizeParticlesEnums
SOP_VolumeReduceEnums
SOP_VolumeResampleEnums
SOP_VolumeResizeEnums
SOP_VolumeSliceEnums
SOP_VolumeVisualizationEnums
SOP_VolumeVopEnums
SOP_VoronoiSplitEnums
SOP_WatershedEnums
SOP_WindingNumberEnums
std
Strutil	String-related utilities
fmt
old
SYS_AtomicImpl
SYS_FastMath
SYS_MathCBRT
Sysutil	Platform-independent utilities for various OS, hardware, and system resource functionality
tbb
Tex
Tf_MakePyConstructor
Tf_PyClassMethod
Tf_PyDefHelpers
Tf_PySingleton
TfPyContainerConversions
TfPyOptional
TfType_WrapHelpers
tinyformat
detail
UT
Format
Detail
Impl
Literal
UT_AbortableLockImpl
UT_Compare
UT_CovarianceMatrix
UT_GeometryPredicate
ut_internal
UT_MemLeakDetectorImpl
UT_NonCopyableNS
UT_Package
utils
UT_Permute
UT_Relacy
UT_ScopeGuard
UT_TimeGateImpl
UT_TupleUtilImpl
UT_VDBUtils
VEX
Literal
VEX_DataObjID
VEX_Geo
VIS_Flags
Vt_HashDetail
Vt_WrapArray
Xdr
XUSD_HydraUtils
xxhash