What is Tense?

tense (noun): 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).

Tense is a method that we use in English to refer to time—past, present and future. Many languages use tenses to talk about time. Other languages have no tenses, but of course they can still talk about time, using different methods.

So, we talk about time in English with tenses. But, and this is a very big but:

• we can also talk about time without using tenses (for example, 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 (see Tense & Time for more about this)

Here are some of the terms used in discussing verbs and tenses.

Mood

Mood

indicative mood expresses a simple statement of fact, which can be positive (affirmative) or negative

• I like coffee.
• I do not like coffee.

interrogative mood expresses a question

• Why do you like coffee?

imperative mood expresses a command

• Sit down!

subjunctive mood expresses what is imagined or wished or possible

• The President ordered that he attend the meeting.

Voice

Voice shows the relationship of the subject to the action. In the active voice, the subject does the action (cats eat mice). In the passive voice, the subject receives the action (mice are eaten by cats). Among other things, we can use voice to help us change the focus of attention.

Aspect

Aspect expresses a feature of the action related to time, such as completion or duration. Present simple and past simple tenses have no aspect, but if we wish we can stress with other tenses that:

• the action or state referred to by the verb is completed (and often still relevant), for example:
  I have emailed the report to Jane. (so now she has the report)
  (This is called perfective aspect, using perfect tenses.)
  
  
• the action or state referred to by the verb is in progress or continuing (that is, uncompleted), for example:
  We are eating.
  (This is called progressive aspect, using progressive [continuous] tenses.)

source : www.englishclub.com