Tangible
Something that exists in the physical world and is capable of being perceived through the physical senses such as sight or touch.
One thing to note is that physical items have certain inherent limitations, such as limited quantity.
Examples: apples, oranges, gold coins, real estate
Abstract
Something without any physical form that lacks the capability of being perceived through the physical senses.
One thing to note is that you can have any amount of abstract items because abstract items can transcend the inherent limitations of tangible items. This is especially so when you maintain the abstract item in an abstract form, such as storing them electronically.
Examples: thoughts, ideas, feelings, concepts
Abstraction
To transform something tangible into something abstract.