根据英国著名的朗曼出版社出版的《朗曼应用语言学词典》所给的定义是：
The use of a second or foreign language in school for the teaching of content subjects.
Bilingual education programs may be of different types and include:
a) the use of a single school language which is not the child’s home language. This is sometimes called an immersion program.
b) The use of the child’s home language when the child enters school but later a gradual change to the use of the school language for teaching some subjects and the home language for teaching others. This is sometimes called maintenance bilingual education.
c) The partial or total use of the child’s home language when the child enters school, and a later change to the use of the school language only. This is sometimes called transitional bilingual education. “双语教学”项目可以有不同的形式，包括：
A) 学校使用一种不是学生在家使用的语言进行教学。这种模式称之为：浸入型双语教学。
B) 学生刚进入学校时使用本族语，然后逐渐地使用第二语言进行部分学科的教学，其它学科仍使用母语教学。这种模式称之为：保持型双语教学。
C) 学生进入学校以后部分或全部使用母语.
简言之，“双语”和“双语教学”的界定是：将学生的外语或第二语言，通过教学和环境，经过若干阶段的训练，使之能代替，或接近母语的表达水平。例如：加拿大奎北克省，同时使用法语和英语，并以法语为其官方语言一样。更通俗地打个比喻，某个西藏同胞既可以在家里用藏语和家人交流，也可以用汉语在工作单位与同事交流。