Upamana is a pramana recognized by the Mimansikas as similar to Nyayikas’ views. In upamana, knowledge of an object is determined by comparing it form other similar kinds of objects. Thus roughly it is treated as analogy. For example,assume a situation where a man has not seen a gavaya or a wild cow and doesn’t know what it is. A forester told him that a wild cow is an animal like a country cow but she is more furious and has big horn in her forehead. In a later period he comes across a wild cow in a forest and recognizes it as the wild cow by compairing the descriptions made by the forester. This knowledge is possible due to the upamana or comparison. Thus, upamana is the knowledge of the relation between a name and the object it denotes by that name.
(Source: BPY005/Block 1/Unit 5/Page 63)