DSLRs are designed to allow you to change the lens. They are offered as "body-only" for people that already have compatible lenses, or know exactly what they want.

Most folks who are new to DSLR want to buy a complete camera, body and lens. So all the manufacturers offer a combination of the body with a cheap lens. This is the "kit lens"

For entry level DSLRs, i.e. the Canon Rebel series or the equivalent in other brands, the kit lens is usually the EF-S 18-55mm F3.5-5.6 lens. Its a starter lens. It sells retail for about $100. This is in fairly stark contrast to many popular lenses, such as the EF-S 17-55 F2.8. At a quick glance, these two lenses seem very similar, same basic zoom range. But the EF-S 17-55 F2.8 sells for $1100, so its ten or eleven times more expensive.

In general, the kit lens is the cheapest lens that the manufacturer can make, and it will satisfy an entry level user. Many folks stay happy with the kit lens for years. Others want something faster, with better image quality, better build quality, etc. Its a personal choice.