The 74 series are a pervasive family of TTL integrated circuits. Originally created by Texas Instruments, eventually all the other major IC producers eventually offered compatibly-functional and -numbered TTL chip lines of their own (so that, say, a 7400 from Motorola was a pin-compatible replacement for the TI chip).
The original 74 series chips (which have numbers of the form '74xx') were joined over time by many other compatible families. '74H' used more power, but were faster; '74L' use less, and were slower. '74S' (using Schottky circuits) which were faster followed, along with '74LS' (low-power Schottky), not as fast as 74S, but using less power. Later '74AS' ('Advanced Schottky) and '74ALS' were added.
The following table gives typical propagation delay (in nsec) and power consumption (in mW):