Why MMIC stands for Monolithic Microwave Integrated Circuit. "Monolithic" means the whole amplifier, including its matching and bias networks, is fabricated on a single chip of semiconductor material (often gallium arsenide), and "microwave" reflects that these devices are built to work at UHF and microwave frequencies. A typical MMIC is a small gain block with 50 ohm input and output impedances, so it needs only a DC bias resistor and blocking capacitors to become a working amplifier stage.
Watch out Choices built around "multi-mode" or "mode modulated" borrow radio operating terminology that has nothing to do with chip construction; MMIC describes how and where the device is made, not what modulation it handles.
MMIC = Monolithic Microwave IC: one chunk of chip, microwave gain block, 50 ohms in and out.