It is the set of forms of verb to indicate time...
its of 3 types - Present Tense, Past Tense, Future Tense

now each tense are divided in 4 sub-parts
Present Tense - Simple Present Tense, Present Continuous Tense, Present Perfect Tense, Present Perfect Continuous Tense
Past Tense - Simple Past Tense, Past Continuous Tense, Past Perfect Tense, Past Perfect Continuous Tense
Future Tense - Simple Future Tense, Future Continuous Tense, Future Perfect Tense, Future Perfect Continuous Tense
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There are 3 types of Tenses are past tense , present tense , and  future tense