What does these Gerber file mean?

What does these Gerber file mean?



ExtensionGerber File
GTLTop Layer
GBL              
Bottom  Layer 
GTO              
Top Over Layer (Silkscreen)
GBO        
Bottom OverLayer (Silkscreen)
GTS      
Top Solder mask

GBS

Bottom Solder mask

TXT
Drill File
DRI
Drill Station Info File
GPI
Photoplotter Info File
GML
Mill Layer
GTP
Top Paste
GBP

Bottom Paste