What does it mean to "shff fh nair into knee?"

Solution 1:

They were trying to tell you to

Short Hop Fast Fall to land the First Hit of Neutral-Aerial which will combo into the Knee of justice.

Phew. Wasn't that a mouthful? But damn is it worth it for the true combo!

There are actually quite a few shorthanded phrases that have been developed for Smash over the years. I've tried to come up with a not-quite-comprehensive list below of acronyms that may be hard to google. I’ve included wiki links where I could find them. You'll hear many of these from tourney commentators as well as written online:

• AC - Auto Cancel
• Bair - Back Aerial
• BKB - Base Knockback
• DA - Dash Attack
• Dair - Down Aerial
• DBZ - When both characters hit each other and are launched at high speed toward the blastzone simultaneously. Usually results in at least one of the two losing a stock. (See Top 10 DBZ Moments)
• DI - Directional Influence
• DJ - Double Jump (using both jumps in quick succession from the ground)
• DSR - Dave's Stupid Rule (used in tournaments for stage picking)
• Fair - Forward Aerial
• FD - Final Destination
• FF - Fast Fall
• FH - First Hit (the first hitbox of a multi-hit move) or Full Hop (opposite of shorthop) depending on context.
• JC - Jump Cancel (usually followed by what you're jump cancelling into. ie: JC Up-Smash)
• JV - Winning with a stock with no damage (so if you won with 2 extra stocks, but were at 0%, it's almost as if you had 3 stocks. You "JV 3-stocked" the opponent. See this Reddit thread for the history behind it)
• KB - Knockback
• KO - Knockout
• MU - Matchup
• Nair - Neutral Aerial
• OoS - Out of Shield
• PS2 - Pokemon Stadium 2
• SD - Self Destruct
• SDI - Smash Directional Influence
• SH - Shorthop
• Zair - Z-Aerial or "Grab Aerial"