It is basicly a dissection puzzle consisting of seven flat geometrical shapes called "tans". The objective of the puzzle is to put together these tans and form a specific shape using all seven pieces, which may not overlap.
Last week I remembered this all of a sudden and found the chart below to make my own Tangram. You can also use it to make yours. The shapes used are: 2 large right triangles, 1 medium right triangle, 2 small right triangles, 1 square and 1 parallelogram.
And some of my homemade creations below :) By the way there are more than 1 billion possible combinations that can be made with only seven tans! I also recommend you to read about tangram paradoxes such as "the two monks paradox", "the magic dice cup tangram paradox" or "clipped square tangram paradox".