Hey, don't feel bad about asking beginner questions.  We all have to
start out somewhere, right?  The good news is that we've all had the
same questions at some point.

First, let's get clear on what a segment is--you are correct that it
is a section of a network bounded by bridges routers or switches.  But
it is also a continuous electrical circuit that is also connected to
other such segments.
So far you are correct.  

Mesh topology involves hooking routers together in such a way that
there are multiple redundant connections or circuits between each
router.  Suppose that you have 5 routers.  Each of those routers will
be connected to each other.  1 will be connected to 2, 3, 4, and 5.  2
will be connected to 1, 3, 4, and 5.  This way you have a whole bunch
of redundant connections so that if one connection or segment or
electrical circuit (whichever term you want to use) fails then there
are other ways that the router has to be able to get it's information
out to the intended destination.  That is what is meant by
fault-tolerant.  Just think of it that way and it's not so confusing.
Sometimes segment can mean different things depending on the context
which we use it in.

The thing with bridges is a little different.  Do you know about
collision domains and broadcast domains?  Bridges reduce collision
domains because they split a segment up into smaller segments(remember
you can also think of it as a circuit).  But they can extend the
segment in another sense because they don't block broadcasts.
Normally, when a computer just needs to talk to somebody on its own
small segment the bridge keeps that communication traffic within the
small segment.  However if it needs to make a broadcast for some
reason, like to find a certain MAC address, the bridge does not
contain that and it goes out across the bridge.  So here's the
problem.  On the one hand, you might think that you're doing good by
splitting up the network into smaller segments by adding a bridge.
But what you've actually done is extend your broadcast domain.
Picture this:  Human Resources and Accounting are on the same segment.
They have a slow network because of so many collisions.  So you put
in a bridge to put each department on their own segment.  You don't
have so much traffic going between Human Resources and Accounting.  So
you feel free to put some more computers on the Human Resources
segment and a few more on Accounting's segment because you want to
take advantage of the speed increase.  Well when they are doing their
normal thing like exchanging files within their own departments on the
same segment there's no problem because the bridge contains the
traffic within it's own segment.  But should one, or heaven forbid,
all the computers all of a sudden decide to start broadcasting for MAC
addresses or something you've now got a problem because the bridge
will not contain all the broadcasts.  So now you're back to having one
segment in that sense.  But since you've added more computers you've
actually extended the segment.

That isn't how it always happens, but it's just one possible scenario
that will hopefully help you to visualize how bridges can extend a
segment and also shorten it.  Kind of weird huh?  Man, that still
sounds confusing.  Hopefully it helps.  If not, then go ahead and
e-mail me to ask more questions.  It's not a problem.  Good luck and
keep learning!