IQF stands for “individual quick frozen.” Individual because the pieces of fruit are frozen separately so they stay separated out of the freezer and you don’t have to deal with a big block of fruit.
All fruit is mostly water. When that water is frozen slowly, it has time to form large ice crystals that tear through delicate fruit cells. Defrosted, the fruit is mushy thanks to its shredded insides. Quick freezing keeps ice crystals small so they do minimal damage to the fruit keeping it in good quality when it defrosts.