Standard cell
Beginner
A small, ready-made building block that a chip is assembled from, such as a tiny yes/no circuit or a one-bit memory.
Novice
A small, pre-designed circuit, such as a logic gate or a flip-flop, drawn once and reused thousands of times. All cells in a library have the same height so they line up in rows, and most come in several sizes: bigger ones are faster but take more area and power.
Expert
A ready-to-place cell with a layout outline (LEF) for placement and routing and Liberty models for timing and power. Each function comes in several drive strengths (X1, X2, X4) and often several threshold-voltage flavors that trade speed for leakage. Synthesis picks function, size and flavor for every instance; a dont_use list keeps unwanted cells out.