The ODbL is a license written for OpenStreetMap. Like a lot of other open licenses, it's not tried in court.
It's a 'sharealike' license: the main important provision is that combining ODbL data with other data requires the combined product to be licensed under the ODbL. In this way it's quite a bit more like the GPL and other old-fashioned open source licenses than MIT or BSD, and much less a license like Public Domain.
Why shouldn't you use ODbL for your project?
The sharealike provision is overly broad and has destructive consequences for potential large users: using derived works from an ODbL database, like geoocoding, routes, images, and so on, could make the entire new work under the ODbL. So, for instance, if you had a restaurant rating site, and you integrate geocoded locations into it from OSM, your entire database, including user data and reviews, may have to be 'opened'.