The basic types
A magnetic kitchen timer sticks to a fridge or oven, so it is always where the cooking happens. A loud kitchen timer is for noisy kitchens or for cooks who are hard of hearing. A professional kitchen timer usually means more than one channel, so several dishes can be timed at once.
What buyers ask about
Buyers ask about display size and readability at a distance, about volume, about whether the timer counts up as well as down, and about how it is powered and mounted. None of those figures are stated here; they are specification questions for the inquiry.
Kitchen timers and the wider timer line
Kitchen timers are one branch of the timer line on this site. Countdown timers, light timers, 7-day timers and outdoor timers are covered in their own guides, because each serves a different job.