A distribution that is a "Mixture model" has a very similar definition as a "multimodal" distribution.
a multimodal distribution is a continuous probability distribution with two or more mode
Now to compare:
In statistics, a mixture model is a probabilistic model for representing the presence of subpopulations within an overall population, without requiring that an observed data set should identify the sub-population to which an individual observation belongs.
What is the difference between the two? They sound like they are the same thing!