Squishy( adjective): 1 being soft, yielding, damp

2 not firm, steady, or fixed ( Definition comes from merriam-webster)

From: “Some people might not be charmed by an experiment that relies on squishy concepts like beauty and happiness.” In this sentence, squishy should mean not steady because it says that people might not be attracted by this results of an experiment which means the result is not steady. People might have different ideas.

In addition, I’ve found another meaning of squishy, to describe a really cute old people, typically little old man, or someone of a huggable nature. From Urban Dictionary. Obviously, those are not best explanations in this condition.