There are three classifications of status moves: non-volatile status, volatile status, and volatile battle status. For the purposes of this answer, "secondary status effects" is taken to mean volatile status conditions, as that's the most common use of the phrase. According to Bullbapedia:
A volatile status is a status condition that is inflicted by a move or Ability from another Pokémon and will wear off when a Pokémon is switched out of battle or when a battle is over. Many volatile status conditions will also wear off after a number of turns have passed. A Pokémon can be affected by multiple volatile status conditions at a time. A volatile status condition is not indicated by an icon.
This list is intended to provide a brief overview of each condition, and is by no means a definitive resource for the mechanics of each one. There are Abilities, moves, and types that can nullify the effects of a volatile status condition -- note that these are not discussed.
Ability change/suppression - Pokemon's Ability is changed or removed during a battle.
Bound - Pokemon cannot switch out or flee. Pokemon takes damage at the end of the turn.
Can't escape - Pokemon cannot switch out or flee.
Confusion - Pokemon will sometimes deal damage to themselves instead of executing a chosen move.
Cursed - Pokemon inflicted with a Ghost type Curse will take damage every turn.
Drowsy - Pokemon will fall asleep next turn if kept in battle.
Embargo - Pokemon cannot use held items or Fling. Trainer cannot use items from the bag.
Encore - Pokemon must repeat its last move used for a few turns.
Flinch - Pokemon will be prevented from attacking for one turn.
Grounded - Pokemon loses its immunity to Ground type moves.
Heal Block - Pokemon is unable to heal for five turns.
Identified - Ghost Pokemon can be hit by Normal and Fighting moves. Dark Pokemon can be hit by Psychic moves. Modifiers to evasion are disregarded.
Infatuation - Pokemon will not be able to move half the time.
Nightmare - Deals passive damage to a sleeping Pokemon every turn.
Perish Song - Pokemon will faint three turns after the move is used.
Seeded - Deals passive damage to an afflicted Pokemon every turn.
Taunt - Pokemon will not be able to use status moves.
Telekinesis - Pokemon is immune to Ground moves, Spikes, Toxic Spikes, and Arena Trap. Most moves used on a Pokemon affected by Telekinesis will always hit.
Torment - Pokemon will not be able to use the same move twice in a row.
Type change - Pokemon's type is changed or removed during a battle.
Exclusive to Legends: Arceus
Splinters - Damages Pokemon at the end of the turn.
Power Boost - Increases Pokemon's damage output.
Power Drop - Decreases Pokemon's damage output.
Guard Boost - Increases Pokemon's defensive stats.
Guard Drop - Decreases Pokemon's defensive stats.
Volatile status conditions (Bulbapedia)
