一、含义
介词是一种用来表示词与词, 词与句之间的关系的词。在句中不能单独作句字成分。介词后面一般有名词代词或相当于名词的其他词类，短语或从句作它的宾语。介词和它的宾语构成介词词组，在句中作状语，表语，补语或介词宾语。
二、分类
1.常用简单介词：
about, across, against, among, after, at, behind, besides, beyond, by, concerning, beneath, between, despite, except, during, down, for, from, past, than, under, until 等。
2.合成介词：
inside, outside, onto, out of, within 等。
3.短语介词：
according to, ahead of, along with, as for, because of, be means of, due to, in spite of, on behalf of, owing to, with regard to 等。
