An unintentional mistake in writing, usually trivial, sometimes amusing

You wrote this word incorrectly once and you said it was merely an oversight. You wrote the same word incorrectly twice and then three times: that's means it's not just a lapsus calami but it's something you get always wrong

Hai scritto male la parola una volta e hai detto che era solo una svista. L'hai riscritta sbagliata una seconda volta e poi una terza volta, ciò vuol dire che non è semplicemente un lapsus calami ma è qualcosa che sbagli di continuo

On the official conference poster one speaker's name is misspelled. It's obviously just a lapsus calami, but the organization certainly does not leave a positive impression

Sul manifesto ufficiale della conferenza, il nome di un relatore è scritto in modo scorretto. È chiaro che si tratta di una svista, ma l'organizzazione non ci fa certo una bella figura

The story goes that a British man used this expression for the first time in the mid-1600s. He wrote a love letter to his beloved Lady Catherine, signing “Within love” instead of “With love”. When, days later, she told him about his mistake, he just laughed and said: “Oh, it was just a slip of the pen.”
From then on, the expression caught on.