I've read phrases like "All gas turbine engines use pressurized seals for their shaft bearing compartments to keep [...]" but I do not understand what "seals" means. In spanish we haven't a word for it.
Seal means sello mecánico.
Bearings are actually located in sumps (cárter). This picture is taken from this answer. You can see the two sumps:
Sumps are watertight and there are seals between the shaft and the sump, or between the shaft and the bearing to contain oil (lubricant) inside. This is a simple oil seal:
A more complex seal looks like this one:
Turbo engines oil seals are specially selected to bear the high rotation speed of the shafts (wear), and the high operating temperature of the engine core (adjustment and bending). Carbon seals are commonly used.
See on Youtube: Carbon Seals - Turbine Engines: A Closer Look.
"Seal" is used here to mean "closure". Specifically, a seal is a mechanism which prevents gases (or liquids) from crossing a barrier.
For instance, a rotating shaft must be connected to a fixed structure by means of a bearing (which allows it to rotate). If dirt or liquid were to enter the bearings, it would damage the mechanisms inside. Therefore, seals are used to keep dirt and liquids out of the bearings. Here is an example from general machinery: http://www.machinerylubrication.com/Read/838/protect-bearings
Seals are things like this:
they prevent oils and other fluid from contaminating areas where they do not belong (and they prevent impurities from contaminating the oils).
You can see one of these used in this assembly diagram (the "oil seal") to protect the ball bearing assembly: