Birch plywood is a good, inexpensive solution for most general woodworking projects.
The quality of woods and plywoods are determined by grading systems.
Rough Sawn - Sawn on a bandmill or circular saw to approximate dimensions
Prepared - Planed in a sawmill
Surfaced - Only small areas of a board are planed to give the buyer an idea of the color or grain figure of the timber.
Nominal Size - The original size of the stock before cutting.
Finished Size - The true size of prepared stock after cutting.
Through and through - Boards converted by T&T cutting will be plain sawn.
One square edge - Boards will have one square edge and one Waney edge.
Waney edge - Board with the sapwood and uneven edge still present, although the bark will have been removed.
Unsorted - This describes the best grade for joinery quality softwoods. Also called clears or clear and better.
4ths and 5ths - Lower grade softwood stock
First and Seconds - The best grade to look for in hardwoods graded for good quality work. At least 83% of each board will yield clear, defect free usable timber in large areas.
Commons - Second grade hardwood, yielding between 67 and 83% clear timber in smaller lengths. Acceptable for cabinet making and small projects.
The normal grading system uses the letters A, B, C & D, where A is the best quality, with virtually no blemishes and very well sanded. Grade D typically contains up to the maximum number of blemishes allowed.
The letter grades typically come in pairs, where one letter refers to the "better" side, called the face, and the other letter to the back side, opposite the face. As such, a sheet of A-C plywood will be very well finished on the face with a relatively unfinished back. Conversely, construction grade plywood would be C-D (commonly referred to as CDX plywood), which is great for structural use but not suited to be finish material.
Maybe someone should make a sticky out of this one. Seems to be a standard question in this section.
Just remember what my father always said, " Half the people in this world are below average!", and everything in life will make a hellova lot more sense.