The term rush can have several meanings depending on its context.
1) In a general sense, it refers to an intense feeling or state of excitement and activity; as in “he’s always in a rush”.
2) It could also refer to the use of certain substances that produce feelings of exhilaration or euphoria, such as drugs like cocaine which is commonly referred to as "doing lines" or "snorting coke".
3) In its botanical sense, rush refers to a type of grass-like plant with long narrow leaves and growing in marshy places. Examples include the common reed (Phragmites australis), and the sweet flag (Acorus calamus).