Here are the data structures with brief descriptions:

CBC_Param_s	A node in a linked list for storing key-value parameters from the bcs.dat file
CBCContext	Provides execution context for a boundary condition handler
CBCS	Legacy boundary condition data
CBoundaryCondition	The "virtual table" struct for a boundary condition handler object
CBoundaryFaceConfig	Holds the complete configuration for one of the six boundary faces
CBoundingBox	Defines a 3D axis-aligned bounding box
CCell	Defines the vertices of a single hexahedral grid cell
CCmpnts	A 3D point or vector with PetscScalar components
CCmpnts2	A 2D point or vector with PetscScalar components
CCpt2D	A 2D vector of PETSc real numbers (for geometry/coordinates)
CCstart	Defines prescribed body motion using splines
CDualMonitorCtx	Context for a dual-purpose KSP monitor
CFlowWave	Represents a single point in a time-varying flow waveform
CFSInfo	Holds all data related to the state and motion of a body in FSI
CIBMInfo	Holds interpolation and distance information for a single IBM point
CIBMList	Head of a linked list for IBM data
CIBMListNode	A linked list node containing IBM interpolation info
CIBMNodes	Represents a collection of nodes forming a surface for the IBM
CIBMVNodes	Represents a collection of nodes forming a volume for the IBM
Clist	Head of a generic C-style linked list
Clist_node	A generic C-style linked list node for indices
CMGCtx	Context for Multigrid operations
CMigrationInfo	Information needed to migrate a single particle between MPI ranks
Cnode	A generic C-style linked list node for integers
CParticle	Defines a particle's core properties for Lagrangian tracking
CPostProcessParams	Holds all configuration parameters for a post-processing run
CProfiledFunction
CRankCellInfo	A lean struct to hold the global cell ownership range for a single MPI rank
CRankNeighbors	Stores the MPI ranks of neighboring subdomains
CSimCtx	The master context for the entire simulation
CSurfElmtInfo	Information about a surface element for FSI calculations
CUserCtx	User-defined context containing data specific to a single computational grid level
CUserMG	User-level context for managing the entire multigrid hierarchy
CVTKFieldInfo	Stores all necessary information for a single data array in a VTK file
CVTKMetaData