What’s simple random sampling?

Read Tan, Steinbach, & Kumar –

Chapter 2 – Data,

Chapter 3 – Exploring Data

What’s simple random sampling? Is it possible to sample data instances using a distribution different from the uniform distribution? If so, give an example of a probability distribution of the data instances that is different from uniform (i.e., equal probability).

I am sharing what I have. I dont have textbook.