By niche, they are suggesting you focus your domain purchases and development projects on one specific topic. The goal is to pick a "niche" or topic you're familiar with, so that you can use any experience you have to make smart purchases and/or contribute it to developing those domains into $ makers.
For me, I know alot about auto loans and auto financing (specifically subprime). So when I first started out, I bought a bunch of domains with key words centered around bad credit, bankruptcy, auto loan, car loan etc.
Right now I'm developing my first "mini site" - which is basically a way to develop traffic & then convert it to advertising revenue. It can also help increase the resale value of the domain.
Because I know alot about this topic, I feel pretty confident I made some smart domain purchases. The experience I have in this field also makes it easier for me to write content that will bring in search engine traffic and help me develop a website that is actually knowledgable.
There is ALOT to this "Domaining" business. The best advice you can get (and you've already been offered it), is to spend ALOT of time on NamePros.com reading. READ everything and ask questions. PPL here are great.
Here are some good starting points. Find threads and articled about:
- SEO (Search engine optimization)
- Mini Sites (find example sites and wrap your head around what they are)
- Revenue Options (Learn about AdSense, Parking, Affiliate Programs and what they are)
- End User Sales (You need to chase your customers, not wait for them)
Those are a few good topics to read about...but please make sure you spend ALOT of time in the NEWBIE section and the Domain Discussion section. There is so much there.
I'm new to this too but in a matter of days, NamePros.com and the people here opened my eyes up and really taught me alot.
Spend your time here and if you're spending your money, spend it on what you know!
Good luck!