This is the 5033rd most frequent Russian word.
математика
Mathematics.
The word 'математика' is used as the subject of the sentence, indicating a field of study.
Математика — это язык природы.
Mathematics is the language of nature.
Here, 'математика' is in the dative case to indicate the object of the verb 'учусь', which is a reflexive verb meaning 'I learn'.
Я учусь математике каждый день.
I study mathematics every day.
In this instance, 'математика' is in the prepositional case, describing the field related to the problem resolved.