Lisping is /s/ and /z/ sounds are not said clearly. Here’s are some speech training exercises for your lisp…
A lisp occurs when the tongue is either too far forward or too low when making the /s/ or /z/ sounds. Sometimes a person’s lispy /s/ sounds more like a /th/. For others, the lisp sound made when speaking is wet because of the tongue being placed low behind the bottom teeth.
As lisping is considered to be a speech defect within the mainstream, in some cases adults or children with lisps may seek or be given speech therapy to reduce or eliminate their lisps. I am not convinced that this is a good idea or even necessary as the implication for the child is that he or she is not good enough when speaking. While this kind of ‘therapy’ may reduce the lisp, it may potentially cause speech blocks (problems of self-expression) due to feelings of shame and unworthiness developing regarding the voice.
Having a lisp is often stigmatised. This can occur either on a cultural level or within the family unit. In many cases the person with a lisp will internalise the message that his or her speech is inferior to that of others. Thoughts such as ‘I can’t give a speech because of my lisp’ are signs of this kind of distorted thinking that is based on shame-based thoughts.
My own view is that a lisp does not stop you from achieving anything in your life. Only your thoughts about your lisp being a problem and something that has to be fixed before you can do x, y and x are what’s holding you back.