Dual-band means it can use either the very congested, but widely supported 2.4GHz frequency, and the seldom-used (because devices that support it are uncommon) thus faster 5GHz band. Simultaneous means it can do both at the same time.
http://en.wikipedia.org/wiki/Mimo - basically each extra antenna increases your speeds, so long as both devices have that many. 2x2 (two transmit, two receive) is common on laptops and some tablets, but cellphones usually only use 1x1 for space reasons.