From wikipedia, a “Bus Factor” is:
an irreverent measurement of concentration of information in a single person, or very few people. The bus factor is the total number of key developers who would need to be incapacitated, as by getting hit by a bus, to send the project into such disarray that it would not be able to proceed
From my personal experience, I'd say that more than 70% of projects suffer from a bus factor of 1. It only takes one specific person in those teams to not be able to be there for the project to halt or slowly die in painful agony as people try to makeup for lost knowledge.
in your mind, go through each person in your team and ask yourself if
the project could go on pretty much as usual if they were fired tomorrow. (fired is important because people who leave in good terms can still play ball and get you through tough stuff they worked on through phone conversations).
If you say “no” or even hesitate about the answer, you’ve found the bus factor in your team.
Most of the collaboration techniques you’ll find in many agile methodologies like XP try to solve the idea of the bus factor, but you don’t have to be agile to use those techniques.
As a team leader, you might just be the biggest bus factor carrier of them all. What happens if you get fired tomorrow? can the team go on without you?
Your biggest challenge as a team lead, over a long period of time would be to make yourself dispensable – to make the team mature enough to continue on day to day things without needing you. Removing yourself as a bottleneck is one of the best things you can do for yourself and your team.