Is the phrase lift weights a correct English if yes why then dictionaries have no definition for it?

Yes, "lift weights" is a perfectly correct phrase in English. It's a common and widely understood expression for the activity of using weights for exercise.

Here's why dictionaries might not have a specific definition for it:

* It's a collocation: "Lift weights" is a combination of two common words that create a specific meaning. Dictionaries usually focus on defining individual words, not common phrases.

* It's assumed knowledge: The meaning of "lift weights" is widely understood, especially by those familiar with fitness and exercise. Dictionaries often prioritize defining less familiar words.

* Contextual understanding: The meaning of "lift weights" is clear from the context of its use. It's usually used in discussions about fitness, exercise routines, or gym activities.

While you might not find a specific definition for "lift weights" in a dictionary, its meaning is clear and commonly understood in the English language.