This area has two parts:
Receptive Language: How we understand what is said to us, our ability to comprehend.
Expressive Language: How we express our thoughts and ideas in words, phrases and sentences.
If your child is having difficulty understanding spoken language, this is likely going to have trouble expressing themselves, too. This likely is a receptive/expressive language disorder. But, if your child seems to understand perfectly but still has a hard time organizing their thoughts into sentences, they would have an expressive language disorder.