In the mobile game, Magic the Gathering: Puzzle Quest, cards can have Renown. What does the Renown keyword mean for MTG: Puzzle Quest?
From the official site, Renown does the following:
Renown triggers the first time a creature with renown deals combat damage to a player. The ability puts some number of +1/+1 counters on that creature (the number after the renown keyword). Also, it causes the creature to become renowned. So, if your Rhox Maulers deals combat damage to your opponent (and trample may help there), it will beef up to a mighty 6/6. Now that it's renowned, its renown ability will no longer trigger, but it will get a better effect from Enshrouding Mist.
Since a Planeswalker counts as a player, damage to a Planeswalker will also activate the Renown keyword.
I found a glossary for the terms in the game, and for renown it states:
The first time this creature deals damage to a Planeswalker, gain +X/+X where x is equal to its Renown value
I also found a discussion between players that seems to confirm this:
Renown adds +x/+x to a creature when it deals damage to the enemy opponent.