'significant' is often used as an adjective meaning noteworthy, important, or influential.
There was a significant decrease in their profits this quarter.
He made a significant change to the original plan.'
He made a significant contribution to their success.
when using 'significant' as an adjective, it is important to also use quantifying adjectives to provide more detail as to the degree of significance. Common mistakes to avoid when using this word as an adjective include using it to describe things that are of little importance and misusing it as a noun.