TENSE

In grammar the word 'tense' means time. It is applied to verbs because verbs indicate time.

A form of a verb used to indicate the time and sometimes the continuation or completeness of an action in relation to the time of speaking ( from Latin: tempus- time)
It refers to time: past , present, future.
In English, we talk about time with tenses.
It gives an indication of when something happens;
We can also talk about time without using tenses (for ex. Going to is a special construction to talk about the future, it is not a tense)
One tense does not always talk about one time
 
Present Tenses 

• Present Tense Simple 

• Present Tense Continuous

• Present Perfect Simple 

• Present Perfect Continuous

Past Tenses 

• Past Simple 

• Past Continuous

• Past Perfect Simple

• Past Perfect Continuous

Future Tenses 

• Future Simple 

• Future Continuous

• Future Perfect Simple 

• Future Perfect Continuous

• Future in the Past