This relates to the words that your child uses and how they put them together using the rules of grammar to express themselves.
Children may struggle to express themselves if they do not have the vocabulary needed for what they want to say. Children may also have difficulty 'finding' the correct word to express themselves. Some children may find it difficult to put words in the correct order and may miss out words within their sentences e.g. 'car drive' instead of 'Mummy is driving the car'.