Frame delay is the time difference between an input being given and the result being executed in an online game. In other words, it is the amount of time it takes for an attack to actually begin after the button has been pressed.
Frame delay is often confused with Wi-Fi lag, though it is in fact closely connected with it.
While it's possible to have no lag in a match, frame delay will always be present, even if by a tiny amount. This makes online matches much more prediction-driven than their offline counterparts.
Brawl Wi-Fi lag
Brawl wifi also shows the extent of frame delay. At the side of every person registered using friend codes, after completing at least one match and quitting (not restarting), a large dot will show up, being colored. People have discovered that this dot refers to the person's connection. The color coding from best (3 frames) to worst (more than 15 frames) is as follows:
Project 64k online lag
Server frame delay is due to the distance between a person and the server. There are 6 different connection types which can change a person's delay. These connections vary due to the amount of packets.
At the start of going on a server, it automatically sets the lag to good but the majority of people who play Smash 64 often are using excellent or LAN connections. These different connections cause different strains on the computer. These connections in other words are better for the higher packet numbers but it takes a larger strain on the computer to run. A connection below 30 ping on an excellent connection, for example, has 3 frames of delay while a connection below 30 on LAN has 1 or 2 frames of delay (1 below 15) while the same connection on good has 5 frames of delay. The majority of people who are used to online Smash can reasonably play on any connection that is better than 6 frames of delay. Excellent is the most common connection since LAN causes problems with some players online.
Player to Player (p2p)
Player to player, which connects one person's connection entirely to another person's connection reduces the amount of delay between players. This is very common to be used between 2 people on opposite coasts, or between a US and a European smasher.
Super Smash Bros. 4
In Super Smash Bros 4, seven frames of delay between pressing the button and the game actually outputting the respective action are always present, regardless of controller, although slower monitors have more input delay.
In Ultimate, roughly six frames of delay between pressing the button and the game actually outputting the respective action are always present regardless of controller, marginally less than Smash 4. The issue of slower monitors having more input delay still exists.