What does "Gunblade" refer to in Netrunner?
The "gunblade" combo refers to having both a Silencer (the gun) + Dagger (the blade) installed. Dagger is strength 0 killer unless a stealth card provides a credit to boost it (+5 for each credit).  Currently, the only stealth cards available that interact with Dagger are Shaper's Cloak (which uses 1 MU, and whose recurring credit can be used on any Icebreaker), and Criminal's Silencer (which is hardware, but can only be used with Killers - and has high influence to splash at 3 pips).  Silencer is prefered over Cloak due to memory limits, which allows you to have multiple Silencers out to stack the ability while also leaving room for other programs.

With 3 Silencers in  a deck and lots of draw (e.g., via Diesel), the idea is that it should come up fairly consistently, and with all the Shaper tricks for tutoring it should be very easy to find/install Dagger. This is a very efficient combo for breaking most sentries, and can be enhanced by Tinkering/Paintbrush to interact with other types of ICE.  Another trick is to boost the strength of Dagger, either via Dinosaurus or Personal Touches to get it to 6+ strength using only 1 stealth credit.