I hear it all the time, and I probably do it myself, but I don't know what that term means. Also, what is I-Spy? Thank you!

Just my viewpoint but to me, Eleanor Burns is the queen of strip piecing. It's when strips are sewn together then cut apart. The pieces are then sewn into blocks. It's a big timesaver compared to cutting out little pieces and sewing them together. I spy is using different or a busy novelty prints and playing a game with a child like, I spy..... an alligator. Then the child finds it.

Another great site to check out for strip pieceing is Cozy Quilt.

You can also consider strip piecing sewing several like pieces together at once. Stack your pieces, HST or such and sew several together without breaking thread before moving on to the next step in you blocks.

I-spy quilts are scrappy using novelty prints, one of each print, so a child can play the I-spy game with it.

Another twist is where there are 2 patches of the same fabric so they can play a matching game.

I've always thought of strip piecing as any patchwork that starts out by cutting strips then sub cutting into smaller patches, often after sewing 2 or more strips together first.

Strip piecing - if you take two jelly roll strips and sew them together then cut out pieces from that - that is strip piecing - so if you want a four patch you sew the two strips together then cut your patches from the sewn together strip - same idea with 9 patch too.
I - spy - I would say that is a quilt made with novelty fabrics so you can "spy" different objects in your quilt - usually a child's quilt.

strip piecing is a bit different than chain piecing but still, it's all sewing as much as possible without removing your work. saves on thread....

They have great patterns and an easy technique and ruler for a strip tube method. She has a few utube videos demonstrating some of their patterns and that method.

When sewing two strips together and sub cutting it. Is a whole lot faster than sewing squares together. I have been using scraps and had to sew lots of squares together for several quilts.