OK, so imagine you have a really big puzzle, but the pieces are all shaped like triangles. But instead of putting the pieces together on a flat surface like a table, you want to build a house or a structure with these pieces.
A reciprocal frame is a special way to put these triangular pieces together to make a strong and stable structure. Instead of just stacking the triangles on top of each other, you make them interlock with each other like a puzzle, but in a special way.
Think about making a pyramid with blocks. You stack them up, but they only stay together because the blocks are resting on top of each other. If you took one block out, the pyramid would tumble.
But with a reciprocal frame, the triangular pieces interlock vertically and horizontally - just like when you lock your fingers together. That way, each piece is supported by the ones around it, making it much stronger and stable.
Reciprocal frames are used to make all sorts of cool things like roofs, bridges, and even treehouses. They're also really fun to build with, but you have to be careful since the pieces can be sharp and heavy.