Used to repair magical items.
- Ron used Spellotape to hold the pieces of his broken wand together throughout 1992, but while it allowed the wand to operate, the wand malfunctioned frequently (CS6).
- Hermione used it to control her copy of The Monster Book of Monsters (PA6).
- Ginny used Spellotape to mend her battered copy of One Thousand Magical Herbs and Fungi (GF10).
- Kreacher used it to mend his photograph of Bellatrix Lestrange (OP23).
- Harry also finds some in Dolores Umbridge’s office at the Ministry of Magic when searching for the locket.
"Spellotape" is a play on words which is lost to Americans. Rowling is making a reference to Sellotape, a familiar brand in Britain.
Sellotape is "a British brand of transparent, cellulose-based, pressure-sensitive tape, and is the leading brand in the United Kingdom. Sellotape is generally used for joining, sealing, attaching, and mending." The name is used generically for household tape in the same way that "Scotch tape" is used in the US (Wikipedia).