What does MOA mean in warframe?

it's a Corpus enemy type, the two-legged chicken-walker robots you see in pretty much every Corpus mission. so if someone says 'watch the moas' they mean those. you can also get one as a companion. on Fortuna (Venus) there's a vendor called Legs who builds MOA companions from parts, you unlock it by ranking up with Solaris United. if a mission or guide mentions moa parts, that's what it's for.