Because I chose the one day minecraft is having errors opening to start a blog about minecraft, I'll be using stock images from the internet to explain powered blocks.

So here you see a leaver (A) powering the blocks around it making them and super-powering block (B). When a block is super-powered it powers all adjacent blocks [eg. the lever or (B)]. We also call these regularly powered blocks "weakly-powered" as not to confuse them with super-powered blocks.

Just a note, super-powered blocks are sometimes called "strongly-powered".