According to Wikipedia: "Copyright infringement is the
unauthorized or prohibited use of works under
copyright, infringing the copyright owner's exclusive
rights, such as the right to reproduce or perform the
copyrighted work, or to make derivative works."
I don't always trust them as a source but that is a
good definition. It's basically illegally using someone
else's work, either to make money for yourself or in
some other way that they have legally deemed
unacceptable.
That could mean using someone else's visual work to
advertise without permission, selling or giving away
someone else's work without permission, or just
plagiarizing.
What exactly is the situation?