English language uses collocations, lexical chunks, and idioms that frequently occur together rather than just individual words. Collocations refer to groups of two or more words that commonly go together, such as "high earnings" and "long-range planning", though there is often no logical reason for the grouping. Lexical chunks are strings of words that function almost as a single unit, including fixed phrases like "over the moon" and semi-fixed phrases that allow some variation. Idioms are phrases where the overall meaning cannot be understood from the individual words, such as "full of beans" meaning energetic. These multi-word expressions cause difficulties for learners.