Makers add liquidity to the order book.
When you place an order that goes on the order book partially or entirely, any subsequent trades coming from that order will be treated as “maker” trades.
These orders add volume to the order book, helping to "make the market", and are therefore termed the "maker" for any subsequent trades.
Takers remove liquidity from the order book.
When you place an order that matches and executes immediately, by filling partially or entirely before going on the order book, those trades will be "taker" trades.
Trades from Market orders are always Takers, as Market orders can never go on the order book. These trades are "taking" volume off of the order book, and are therefore called the "taker".