Tinlok is dually licenced under the GNU Lesser General Public License version 3.0 or later, and the Mozilla Public License Version 2.0 or later.
What this practically means:
No matter what, if you modify the source code of this library and redistribute it, you must provide the modified source code.
If your library or application uses Tinlok statically linked (i.e. as a Kotlin application, or statically linked into your own library), if the LGPL is chosen your code will also be subject to the LGPL. If the MPL is chosen no such action applies.
This is primarily a concession to people who won’t use copyleft licenses. If Kotlin ever gets dynamic linking for Kotlin applications, rather than having the klib directly included, the MPL will be removed and Tinlok will become purely LGPL.