Acceptance must be ABSOLUTE as per the Indian Contract Act, 1872.
It means that the acceptance should be without any condition. Acceptance with a condition does not count to mere acceptance but is termed as a counteroffer or a counter-proposal.
If the offeree has signed acceptance with a condition, then in such a case the contract is not enforceable till the proposer accepts the variance. This is an example of a counter-proposal but is not considered as acceptance.
Absoluteness also means that the offer must be communicated without any variation, so then acceptance made is considered absolute. If an offer has not been communicated, then in such case the acceptance can be revoked and the acceptance is not absolute.
Acceptance must also be done without any duress or any kind of undue influence. In such cases, the contracts are voidable, if the acceptance is done while being kept under some kind of duress or influence. And the acceptance can also be not considered as absolute acceptance.
If acceptance is given with false conditions then the contract is not enforceable and since the acceptance was given under false conditions, the acceptance cannot be considered absolute and the acceptance is revoked.
In conclusion, acceptance can be considered as absolute when acceptance has been given without any variance, the conditions have been communicated between the parties, the acceptance has been given without any party being kept under duress or any undue influence, and also when the acceptance is given without any party being under pretenses.