KINDLY explain to me what selectively permeable means in simple words like really simple cause am revising cell stuff

Well ,Selectively permeable means a membrane allows the passage of some molecules or ions and inhibits the passage of others. The capacity to filter molecular transport in this manner is called selective permeability. or a property of cellular membranes that only allows certain molecules to enter or exit the cell. ... Movement across a selectively permeable membrane can occur actively or passively. ( best example would be ) For example, water molecules can move passively through small pores on the membrane.

Explanation:

hopefully that made sense they're really isn't a shortcut on explaining this type of topic but i tried to make it as understanding as possible, Good luck! :)  

name and explain one of the event that occurs during meiosis that increases the variation in offspring even more than simple reproduction?