Semantic holism means that the meaning of a word or a sentence is determined by the entire context in which it is used, rather than just by the individual words themselves. It's like putting together a puzzle - each piece of the puzzle is important, but the overall picture is what makes sense.
For example, let's say you're trying to understand the word "cat". If someone just says "cat," you don't really know what they mean. But if they say "I have a cat," you can start to understand what they're talking about. And if they continue and say "My cat is black and white, and it loves to play with string," you have a much clearer picture of what a "cat" is.
This concept applies to sentences and entire conversations as well. The meaning of one sentence depends on the sentences that came before it and the ones that come after it. And the meaning of a whole conversation depends on everything that was said during that conversation.
So, semantic holism means that you can't just look at individual words or sentences to understand their meaning - you have to look at the bigger picture.