Statistical significance is a measure of how unlikely a study's result would be if there were really no effect, usually reported as a p-value.
By convention, a p-value below 0.05 is called significant. It means a result at least that strong would occur less than 5% of the time by chance alone, if there were no real effect.
Significant does not mean large or important. A very large study can find a significant difference that is too small to notice in daily life. That's why good studies report effect size alongside significance.
It also doesn't prove the result is true. One significant finding can be chance, especially when a study tests many things at once. Look for results that have been repeated in other studies.