A White Noise Machine is a device that produces a consistent and soothing sound that will mask out unwanted and disturbing sounds.
Some of the simpler ones make a noise that is similar to the hiss noise that comes from a tv station that is off the air with snow on the sceeen.
Some of the more elaborate ones will make 20 or more different noises, like a babbling brook, rain, surf, and similar noises.
The idea is to replace the unwanted noise with a neutral noise.
My DW bought ours through Avon 3 or 4 years ago for about $20, it's small and battery operated, ideal for travel. I use rechargeable batteries in it now.
I did a search on the Internet and I found an elaborate one from Sharper Image and the list price is $120. I also found out that Sharper Image has an Ebay Store and you can buy their products at a lower cost through them. Most of the ones offered are 'like new' and are products that have been opened and repackaged, with a full warranty.
I'd suggest doing your own websearch to find one that you would be interested in. I don't think the Avaon model is offered right now, it wasn't in their online catalog.