It is also known as a maintained hypothesis or a research hypothesis
Firstly many hypotheses are proposed. Then among them, one is selected which is the most efficient.
There are four main types of alternative hypothesis:
Point alternative hypothesis: Population distribution in the hypothesis test is fully defined and has no unknown parameters.
Non-directional alternative hypothesis: It states that the null hypothesis is untrue.
One-tailed directional hypothesis: It is only concerned with the region of rejection for one tail of a sampling distribution.
Two-tailed directional hypothesis: It is concerned with both regions of rejection of the sampling distribution.