Wikipedia
Parasolid is a geometric modeling kernel originally developed by Shape Data Limited, now owned by Siemens PLM Software (formerly UGS Corp.), that can be licensed by other companies for use in their 3D computer graphics software products.
Parasolid's capabilities include model creation and editing utilities such as Boolean modeling operators, feature modeling support, advanced surfacing, thickening and hollowing, blending and filleting and sheet modeling. Parasolid also includes tools for direct model editing, including tapering, offsetting, geometry replacement and removal of feature details with automated regeneration of surrounding data. Parasolid also provides wide-ranging graphical and rendering support, including hidden-line, wireframe and drafting, tessellation and model data inquiries.
When exported from the parent software package, a Parasolid commonly has the file extension .x_t. Another format is .x_b, which is in binary format so it is more machine independent and not subject to binary-to-text conversion errors. Most Parasolid files can communicate and migrate only 3D solids and/or surface data - Parasolid files currently cannot communicate and migrate 2D data such as lines and arcs.
To use Parasolid effectively, users need to have fundamental knowledge of CAGD, computational geometry and topology.