A line source generally refers to a line array, such as these:https://www.canuckaudiomart.com/details/649191525-mcintosh-xrt28-line-array-speakers/images/951460/
A point source is either a single, full range driver, or a coaxial speaker like these:https://www.parts-express.com/bc-6fhx51-65-professional-coaxial-speaker-70-x-70-8-ohm--294-5761
In a line source/line array there’s either a very long single driver (see Carver Amazing) or an array of identical drivers arranged in a line (see also Infinity Reference Standard).
A point source is often also a "coaxial." Meaning you have the tweeter sitting in the center of the mid/woofer.
The goal of coaxial and line sources are rather similar, to present a single point in space from which your ear receives the sound. Line arrays do so with the added advantage of having very narrow vertical dispersion, which can often yield better interaction with the room. An advantage to both is that as your ears move around the room, there's no change in relative distances between the tweeter and mid or mid-woofer, so the phase relationships of all frequencies remains constant.
Traditional multi way speakers are neither line arrays nor point-sources, and as you move, by standing up, sitting down or just shifting left to right on the couch, the distance to the tweeter, midirange and woofer is constantly changing.
Usually you’ll see combinations, like a coaxial or line array down to a few hundred Hz, then they’ll switch to a single woofer.
Old Thiel, and current TAD are examples of this hybrid point source approach. They used a tweeter/midrange combination at the top, then switch.