What is the difference between a Business Partner and Co-Founder?

Maybe it's just semantics, but I am putting the word out that my biz will benefit from either.

We have pushed a product off the shelf and are starting to acquire customers, yet the effort has grown too large for me to handle it as efficiently as I'd like and work my day job. I have decided to give up some equity ownership in exchange for finding a partner that will get us to v2.0. This person would possess a complementary skill set.

Does Co-Founder imply more ownership, or is that just a more contemporary way of saying "Business Partner"? Which term do you prefer?

For me the term co-founder implies that the person became a co-owner of the business during the early stages of the business. Whereas the term business partner does not necessarily imply that. For example, let's say in 10 years you bring someone else on board as an owner. I would not consider that person a co-founder, but I would consider them a business partner. In fact, I would say that the term business partner could be used to refer to someone that does not necessarily have equity in the business, but yet has some skin in the game - perhaps they get a share of the profits.

Edit : From dictionary.com:

Founder : a person who founds or establishes.

Partner : a person who shares or is associated with another in some action or endeavor; sharer; associate.

This is mainly semantics.

I have a co-founder in my business, who joined five months after I started. When I have him on a pitch deck for investors, I call him 'Co-Founder' (he does have a significant equity holding as this term implies). When I talk about him with my parents, I call him my 'business partner'.