Yaiba means "the blade of a sword," Keiji Inafune explains in this developer diary for Yaiba: Ninja Gaiden Z. It is, somehow, the subtler component of the protagonist's full name: Yaiba Kamikaze.
Yaiba: Ninja Gaiden Z is being developed primarily by Spark Unlimited, the Los Angeles-based studio also responsible for Lost Planet 3. In the video, Inafune says the studio is "exactly what we wanted" because they were able to bring a unique perspective to the ninja, unifying Western and Eastern visions on the classic archetype. "To appeal to both, it made sense for us to work together."
Inafune then goes into an astute metaphor about how game development is like building a house – at least, we think it's astute. We've never built a house before.