The dictionary definition of facilitation is to make something easier. In this broad definition, facilitation covers a lot of ground. But in the continuous improvement definition, facilitation has a few common characteristics.
Facilitation is generally done for groups, not for individuals.
Facilitation is most common for discrete projects. You might see a facilitator for a kaizen event, but probably not just to help with day-to-day operations.
Facilitation should focus on tools, not processes. A facilitator should walk teams through a decision making process, not make the decision for them.
Facilitation should focus on getting good results, not on implementing a particular method.
Facilitation can be done by a member of the company, or by a professional facilitator. Professional facilitators tend to be better trained than people that do it only occasionally-practice makes perfect.
Bringing in an outsider also has the added benefit of neutrality. Hired facilitators don’t tend to have the bias that a manager or supervisor might have. Note that the outsider in this case can be someone from the company’s own Lean promotion office, or a hired consultant.