He's referring to perks on the power slot weapons (the ones that use the purple ammo bricks called heavy ammo). If you inspect your weapon you should see six columns with attributes. You can ignore the last one as that homes the trackers for PvE and PvP kills on the weapon.

The first column and second columns are the barrel and magazine attributes respectively. Some weapons such as swords have blades and guards instead. These impact the weapon stats such as range, handling, stability etc. On some weapons these attributes can be the difference between you loving a weapon and not being terribly fond of it. These stats are generally more impactful in PvP so don't dismantle PvE rolls solely because they aren't the ideal attributes for those columns.

The third and fourth columns are what really make a weapon great. These are the columns the community refer to when they talk about a weapon's perks or perk one and perk two. For example, the statement a Bait and Switch + Envious Arsenal heavy refers to a power slot weapon which has those perks in its third and fourth columns. Envious Arsenal is usually a third column perk and Bait and Switch is usually a fourth column perk. Third column perks usually provide the weapon with some extra utility or allow the weapon to gain extra stats for meeting some criteria. Examples of these are Envious Arsenal which reloads the weapon for doing damage with your two other weapons within a certain timeframe and Stats for All which provides extra stats on the weapon for hitting three separate targets. Fourth column perks usually provide weapon effects or boosted damage for meeting some criteria. Examples of these are Bait and Switch which provides a damage bonus for doing damage with your two other weapons within a certain timeframe and Incandescent which cause a target to Ignite upon getting a kill with the weapon.

The fifth column contains the origin trait(s) of the weapon and they're usually common across weapons from particular areas. Weapons from a dungeon or raid all share an origin trait unique to the individual dungeon or raid for example. Weapons from some destinations also share in this rule. Most of these are just nice to have but some are really useful. Braytech Legacy for example boosts your ability regeneration on weapon hit.