It wasn’t entirely clear in the parts that I watched, but my understanding is that slime molds are actually “social” amoeba. They often crawl around as loners, eating whatever they can find. But if they run out of food, they start sending out chemoattractants to all of their buddies in the neighborhood. They all crawl together and create a fruiting body (a spore) that eventually will break off in the wind
and land somewhere else. Hopefully, in greener pastures. Those fruiting bodies are what you see in these videos. Amazing creatures, they live on the brink of multicellular eukaryotes.
There are many groups of slime-mold-like living beings and most of them are not closely related and they have evolved independently the ability to make multicellular fruiting bodies, as an adaptation to the life in terrestrial conditions (where an elevated position is needed to enable the dispersal of spores by the wind, like from mushrooms).
In most of these groups, they live as single amoeboid cells and they aggregate into multicellular fruiting bodies only for reproduction. Besides most such groups that are eukaryotes (nucleated cells), there is even a group of bacteria, the Myxobacteria, which have the same ability of making multicellular fruiting bodies.
Besides the many groups of slime-mold-like living beings, with similar mushroom-like fruiting bodies, there is a single group of those which have been known by humans for the longest time and which are the only for which the name "slime molds" (the English translation of Myxomycetes) should be applied in the strict sense.
For the slime molds properly, the term "social amoebae" is not appropriate as it is for the others, which live single and then aggregate into multicellular fruiting bodies.
The true slime molds spend most of their life as multicellular or multi-nucleated (so-called plasmodia) bodies, which are big enough to be seen without magnifying instruments, which is why they have been known many centuries before the others. As seen in the linked videos, the true slime molds are blobs that move slowly around, usually eating bacteria.
