Ranging from "the company that sells the same product as you". And "the company that your customer is spending money on". To something that probably need a doctors hat to understand.
But - maybe we should consider competition as everything that takes away the customers attention that we want. If we have full attention from customer he will listen to us - and only to us. And then we can show him that we care. And also provide the services he need.
The moment something else steals his attention we have competition. And a risk that we get less attention. Leading to less sales and money.
If we define competition as "attention stealers" we can see other forms of competition that stops us from doing business. Maybe the customer is concerned about Global Warming? Sick kids? Financial crisis?
If the customer is worried about Global Warming or his upcoming divorce - will he listen to us? Is he willing to buy our newest product?
If he is concerned about something attention from us is diverted. And thus we are less likely to succeed. We need to deal with all sorts of competition! From competing companies selling the same products - to whatever takes away attention from us.
The classic definitions of competition fit in of course. But there are also other form of competition we need to deal with.