What is language?
Language is a kind of meaning system used for communication and expression. Language can be expressed three different ways, through speech, writing, or signs. Language is something that is unique to humans. The main question linguists have about language is “Where did it come from?” Was it developed by human cognition because of the development of culture? Or, Is the ability for language already wired in the Homo sapiens brain? 
What is “a language?”
The essential features that enable a language to be “a language” include sounds, words and sentences. An example of “a language” could be French, English, Chinese or Hindi. Each one of the languages listed has a specific structure that has to be learned in order to communicate in that language effectively. I took French courses throughout high school and college. In these courses I had to learn the correct structure of a French sentence vs the English structure I was comfortable with. For example, in English I could say “Jane is wearing a red bathing suit” this translates to “Jane porte un maillot de bain rouge” in French. If I were to take this sentence word for word and translate it back to English, I would get “Jane is wearing a bathing suit red.” This is cool because these rules can be recorded, documented and tested. However, when it comes to the idea of language as a meaning system, it is much harder to record, document or test.