When language is learnt naturally and without any systematic practice, it is called:

Language is a symbolic, rule-governed system, shared by a group of people to express their thoughts and feelings. In a child, language development takes place through language acquisition and language learning.

Key Points  

Language acquisition:

• It refers to the subconscious process of learning a native or second language because of the innate capacity of the human brain.
• It is a natural process whereby children acquire language unconsciously by observing and repeating what they hear in the natural/informal setting.
• Language acquisition does not require any formal instruction, children acquire the language without being taught. It is a natural process so, one does not forget one's native language.

Hence, it could be concluded that when language is learned naturally and without any systematic practice then it is called as acquisition.Hint 

• Language learning refers to the result of deliberate and conscious effort for a better understanding of foundational skills of language learning. It takes place in a formal setting.