When you lean in a particular direction, you bend your body in that direction.

If you lean on or against someone or something, you rest against them so that they partly support your weight. If you lean an object on or against something, you place the object so that it is partly supported by that thing.

If you describe someone as lean, you mean that they are thin but look strong and healthy.

If meat is lean, it does not have very much fat.

If you describe an organization as lean, you mean that it has become more efficient and less wasteful by getting rid of staff, or by dropping projects which were unprofitable.

If you describe periods of time as lean, you mean that people have less of something such as money or are less successful than they used to be.