Contextualisation is putting language items into a meaningful and real context rather than being treated as isolated items of language for language manipulation practice only. Contextualising language tries to give real communicative value to the language that learners meet. The context can help learners remember the language and recall it at a later date. Learners can use natural learning strategies to help them understand contextualised language, such as guessing meaning from context.
Teaching the language used to give advice by looking at problem pages from teenage magazines gives the target language context.
In the classroom
Contextualisation can be as simple as providing an example sentence that uses a new word, or as complex as preparing a telephone role-play to practise functional language.