What is the meaning of Lisp?

The habit or an act of lisping.

To pronounce the consonant ‘s’ imperfectly; to give ‘s’ and ‘z’ the sounds of ‘th’ (/θ/, /ð/). This is a speech impediment common among children.

To speak with imperfect articulation; to mispronounce, such as a child learning to talk.

To speak hesitatingly and with a low voice, as if afraid.

to express by the use of simple, childlike language.

To speak with reserve or concealment; to utter timidly or confidentially.

Source: wiktionary.org