Often, people want to encode the name of the package release into the shared library so that it is obvious to the user which package their programs are linked against. This convention is used especially on GNU/Linux:
trick$ ls /usr/lib/libbfd* /usr/lib/libbfd.a /usr/lib/libbfd.so.188.8.131.52 /usr/lib/libbfd.so trick$
On ‘trick’, /usr/lib/libbfd.so is a symbolic link to libbfd.so.184.108.40.206, which was distributed as a part of ‘binutils-220.127.116.11’.
Unfortunately, this convention conflicts directly with libtool's idea of library interface versions, because the library interface rarely changes at the same time that the release number does, and the library suffix is never the same across all platforms.
So, in order to accommodate both views, you can use the -release flag in order to set release information for libraries for which you do not want to use -version-info. For the libbfd example, the next release that uses libtool should be built with ‘-release 2.9.0’, which will produce the following files on GNU/Linux:
trick$ ls /usr/lib/libbfd* /usr/lib/libbfd-2.9.0.so /usr/lib/libbfd.a /usr/lib/libbfd.so trick$
In this case, /usr/lib/libbfd.so is a symbolic link to libbfd-2.9.0.so. This makes it obvious that the user is dealing with ‘binutils-2.9.0’, without compromising libtool's idea of interface versions.
Note that this option causes a modification of the library name, so do not use it unless you want to break binary compatibility with any past library releases. In general, you should only use -release for package-internal libraries or for ones whose interfaces change very frequently.