"The mountain is low."
If the bottom character is ㄷ, ㅌ, ㅈ, ㅊ, ㅅ, ㅆ, or ㅎand it's not followed by a vowel (or followed by one that's from a separate root word), then the sound will be like a "t" that's cut in the throat.
You'll hear the sound of the regular letter when it's followed by a vowel that is from the same root. And the sound will carry over sort-of to that next syllable.
Ex: 맞다 sounds like "맡다" (mat-da) 맞아요 sounds like "마자요" (ma-ja-yo)