What kind of drill bit is this?
That's sometimes called a "drill-saw" bit used for drilling a hole and then enlarging the hole into a slot (or other shape) by applying sideways pressure.

I have a couple of cheap ones and didn't find them very effective in softwood. To make a long slot (1ft or 300mm) I had to drill lots of adjacent holes conventionally and then used this type of bit to join the holes. If I had to do it again, I'd consider buying a cheap router for the job. A hand jab-saw/pad-saw/keyhole-saw might be quicker and might be a similar amount of effort.