Generally there are two types frames for manual wheelchairs: Folding and Fixed.
Folding frames are highly recommended for easy storage, travelling and to fit in cars. The traditional folding frame has the "X" design below the seat (as per Image 1).
Image 1 - Karma Ergo Lite 2 - Transit
By lift the front of the seat upwards the frame will folds in half and bringing the sides together (see Image 2).
Image 2 - Drive Ultra Lite Wheelchair
Rigid Frames, on the other hand, have fixed non foldable components - such as a horizontal bar below the seat (see image 3). Ideal for active users, it is often more compact and has a lighter weight compared to folding frames.
Image 3 - Ottobock Ventus