Referee and Identity

In guidelines, it say

The other referee must be the holder of a British citizen passport and either a professional person or over the age of 25.
Each referee should be:

1. not related to you
2. not related to the other referee
3. not your solicitor or agent representing you with this application
4. not employed by the Home Office

what does that not related to you means number 1 ? if the person doesn't know me ...how come sum1 will give reff

As Professional Reff ...i know an Accountant ....he is my friend from couple of years and now recently had become Accountant (what should I write - how i know him Friend or I am his client) and is it fine to use him Professional Referee.

It must not be a relative of yours like brother, sister, mother, etc..
Accountant is fine and him being your friend or you being his client will both do.

Thanksss so much