"Annual training" is an industry habit, not a federal rule. Some standards do require it; most set triggers instead. Knowing which is which keeps a training calendar honest.
Annual, in the text. Bloodborne pathogens training is required at initial assignment and at least annually thereafter, with each annual session within one year of the previous one (29 CFR 1910.1030(g)(2)(ii)(A)–(B), (g)(2)(iv)). The hearing conservation training program must be repeated annually for each employee in the program (29 CFR 1910.95(k)(2)). Respirator retraining is administered annually and when specified situations occur (29 CFR 1910.134(k)(5)). Fire extinguisher education is given upon initial employment and at least annually (29 CFR 1910.157(g)(2)). HAZWOPER site workers, managers and supervisors receive eight hours of refresher training annually (29 CFR 1910.120(e)(8)).
Triggered, not scheduled. HazCom training happens at initial assignment and when a new chemical hazard is introduced (29 CFR 1910.1200(h)(1)). Lockout/tagout retraining is required on a change in job assignment, machines, equipment or processes presenting a new hazard, a change in the energy control procedures, or when the annual inspection or other evidence shows deviations or inadequacies (29 CFR 1910.147(c)(7)(iii)(A)–(B)) — the annual item in LOTO is the inspection, not the training. Permit-space training is given before first assignment, on a change in assigned duties, on a new hazard, and when the employer has reason to believe procedures are not being followed (29 CFR 1910.146(g)(2)). PPE retraining follows changes in the workplace or PPE, or inadequate understanding (29 CFR 1910.132(f)(3)), and construction fall-protection retraining follows the same logic (29 CFR 1926.503(c)).
On a longer clock. Powered industrial truck operators get refresher training when unsafe operation, an accident or near-miss, an evaluation, or a change in truck or conditions calls for it, and an evaluation of performance at least once every three years (29 CFR 1910.178(l)(4)(ii)–(iii)).
State Plans and company policies often add annual cycles on top of these, and nothing prevents an employer from training more often. The point of the list is to know which annual sessions are required and which are a choice.