Dacron refers to the thin, usually braided or twisted line made from Dacron fibers used for heavy sports fishing and kite flying. It doesn't stretch like nylon, and is somewhat abrasive. Dimensionally I have some 120 lb test that is about the same diameter as 12 lb monofilament fishing line. There are a host of similar synthetic strings out there that are used for much the same thing. Dacron was simply one of the first and is what I happen to have and is usually less expensive than the newer versions. I used 120 lb Dacron line for Halibut and King Salmon fishing up out of Hakai along the inside coast of Vancouver Island quite a few years ago, and it is TUFF STUFF!

I've seen it in weight strength from 50 to 200 lbs, and I think the 100 lb stuff is about ideal for most of us.

If you web search for kite string, you are bound to come across some suppliers. Additionally, we've talked about it on this forum quite a bit in the past; I remember at least two threads where it was discussed.