In computer science, abstraction refers to removing unnecessary attributes and data fro objects or systems in order to focus attention on crucial details. The process can be compared to generalizing something - the more broad and concise something is, the easier it is to understand its function! Abstraction is fundamental to object oriented programming along with Encapsulation and Inheritance.
Through the process of abstraction, a programmer hides all but the relevant data about an object in order to reduce complexity and increase efficiency.
Think about what information could be relevant to a situation where you're meeting a new person: there are several attributes to keep in mind, such as your what you're wearing, your name, your age, and your interests. But these aren't the only characteristics about you - there are other data and information not relevant to the context at hand, like your account login, or your social security number, or what you had for lunch yesterday.
Although, since this information could be used in multiple contexts, you can use these abstractions in other situations in the future!
This is the core of abstraction - keeping relevant information on hand to be used in specific situations, with other data abstracted out to be used in other ones.