Dictionary definition. Significant is an adjective with the following meanings: 1. Having or expressing a meaning; meaningful. 2. Having or expressing a covert meaning; suggestive: Example: She gave him a a significant glance. 3. Having or likely to have a major effect; important: Example: There was a significant change in the tax laws. 4. Fairly large in amount or quantity: significant casualties; Example: The army unit did not encounter any significant opposition.

I'd say you can use the word "significant" when you're stating the difference or emphasizing something. "I found a significant difference in quality between Product A and B." "The flood left a significant amount of damage to our carpet."