If something is slotted, it means it is put into a long, narrow hole or opening.
The word slotted makes people think of things fitting neatly into place.
Examples:
The letter is slotted into the mailbox.
She slotted the coins into the piggy bank.
He slotted the key into the lock.
The book is slotted neatly on the shelf.
The puzzle piece is slotted perfectly into the empty space.
The card is slotted into the deck of cards.