It means you can add as much or as little of a seasoning based on personal preference. Add herbs to the sauce to taste; some like it herby, others don't.
Pro Tip 2/3
Cooking Flexibility
Used often in recipes to indicate the seasoning can be adjusted while cooking. Chili can be spicy or mild, so add the pepper to taste.
Pro Tip 3/3
Not Exact
It suggests that the exact amount is up to the individual, not to follow a strict measurement. Garlic can be strong, add it to taste so the dip isn't overwhelming.