The syntax is the flavour of disassembly syntax prefered to be used by the disasm engine.
Actually the x86 disassembler is the more complete one. It's based on udis86 and supports the following syntax flavours:
e asm.syntax = olly
e asm.syntax = intel
e asm.syntax = att
e asm.syntax = pseudo
The 'olly' syntax uses the ollydbg disassembler engine. 'intel' and 'att' are the most common ones and 'pseudo' is an experimental pseudocode disassembly, sometimes useful for reading algorithms.