The Headset Microphone
The fourth type of mic is a headset mic. This is a small mic, similar to the lavaliere, but it's attached to a headset that usually fits behind your ear. This mic is probably the easiest to use; you almost don't even know it's there. Unfortunately, it has a couple of drawbacks.
The first is cost. Headset mics are expensive, so it's rather unlikely that you'll be supplied with a headset mic when you speak. (You can always purchase your own, but cost is still a factor.)
The second problem is that, although the headset mic is small, it's still visible on your face. As such, it's a distraction, and you may not want it to distract your audience from what you're saying. (Sometimes Broadway actors hide their headset mics in their hair, right at the hairline. I've never tried it, but it apparently works. Of course, you need to have a hairline to do it this way.)
If you look closely, you'll spot this mic used quite frequently by news anchors on the evening news. Singers and other performers also use it a lot, and the number of professional speakers using headset mics is growing every year.