There are a few different concepts of boredom that I feel, which many have touched upon in some form or another.
1. Restlessness in waiting for an event. Being forced to do something you don't want to do, and counting the time until it's over. Mind-numbing is the best way to describe this; it's a passive boredom that once the alotted time is over, you will no longer be bored. (E.g. being lectured, watching a movie you have no interest in, waiting to run a race, etc.)
2. Feeling disengaged and as though there's nothing you can think of to feel engaged. It's kind of restless, something you'd waste an afternoon with a friend over, asking each other what you want to do with no one being able to come up with a suitable reply. (I.e. nothing sounds interesting.)
3. Being engaged and feeling no satisfaction or attachment to what you're doing, even if it's something you usually enjoy, or heck, if you're actually enjoying it you feel unfulfilled and it all seems pointless. Sleep/taking a nap to overcome this provides no relief. I'm not sure if this stems from depression, but I would describe this as existential boredom, and it's not something that's actively overcome easily. This is a boredom borne of dissatisfaction, not purposelessness. (I.e. nothing is interesting.)
4. Purposelessness and finding dissatisfaction because of it.
When I hear people say they're bored, I assume #2 unless I'm in a position of shared context and can infer they really mean #1. I don't believe I've really heard anyone talk about #3. #4 usually involves other qualifiers so there's no confusion in the meaning.