A teacher asks her learners of class-VII to refer to the textbook of History and find a theme which can be connected with English language text for writing an essay. What is this practice known as?

When language learning is connected with content from other subjects (like History), it exemplifies 'Language Across the Curriculum' (LAC). This NCF 2005 concept recognises that language is the medium of all learning and should be developed through all subjects. The teacher's practice of linking English writing with History content is a classic LAC approach, broader than subject-specific integration.