Abstract simplicial complex

An abstract simplicial complex is like Legos! They are built from tiny blocks called "simplices". These simplices are like the little blocks you can build shapes out of. You can put them together to create shapes or structures. You don't see the blocks when you look at the structure, all you see is the shape. You can think of an abstract simplicial complex as a 3-dimensional structure made out of Legos. The blocks are grouped together to create the overall shape of the structure.