Meteor = can be meteor canceled which means you can up b to cancel the downward momentum
Spike = cannot act until hit stun is over (i.e. Falco/Marth's dair)
To elaborate on the mechanics portion of things, meteor smashes are attacks that send the opponent between the angles of 260 and 280 degrees (almost straight down) while spikes are attacks that send the opponent downwards but outside the angles of 260 and 280 degrees (downward at an angle); the hitstun from a meteor smash can be interrupted with a meteor cancel but the hitstun from a spike cannot be interrupted, hence why spikes are generally more effective at gimping/KOing the opponent.
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As others have stated before, Ike's DAir is a meteor smash at the tip, blade, and arm hitboxes while it's a spike at the hilt hitbox. It's a pretty effective edgeguarding tool, since you can either opt for the spike/meteor with an early DAir or
weak DAir -> BAir/FAir with a late DAir. If you want to spike/meteor opponents recovering low, walk-off DAir is generally the best method because of its reach and, if performed as quickly as possible, Ike doesn't need the edge in order to recover if you miss.