Here are some snippets from a Forbes article on premium domains - unfortunately I do not have enough posts to post the link to it.
The top-level domain (TLD) is the string of characters at the end of a domain. To be worth anything at all, a domain name needs to have a good TLD that doesn't compromise your ability to reach potential customers. In general, premium domain names will usually use the .com TLD or a relevant country code that suits the target audience.
Overly long domain names can be harder to remember. Likewise, domains with hyphens or other punctuation can be less successful due to this complexity. Any domain name needs to be concise in a practical sense that makes it more memorable. As a result, premium domain names usually consist of one to two words or two to four individual characters.
Generic value. Many of the most valuable domain sales of all time dealt with domain names that had deeply generic names. For instance, consider CarInsurance.com, which sold for nearly $50 million. This sort of generic value dramatically increases demand thanks to industry-wide appeal, and it serves to amplify value in the process.
Contains keywords and high domain authority. SEO is one of the keys to running a successful web presence in the modern day, and domain names can help. While Google has reported it does not weigh keywords in domain names, I've found it's generally true that domain names with keywords make up an outsized share of the first-page results. There are many potential reasons for this, but it is a trend worth keeping in mind.
Key Concept: Brandability
For the most part, you can understand premium domain names via the concept of brandable. When a domain name is easier to build a brand around, it's more recognizable and, therefore, more valuable. Premium domain names are expensive for the simple reason that the ease with which customers can remember and access them means that they help websites gain a critical advantage in today's competitive marketplace.
A premium domain name is one that had been used in the past but is currently available. It will have a familiar top-level domain such as .com, .net, .biz or .org. The domain will be simple, easy to remember and can work wonders for your business.
The pricing will vary depending on certain criteria that determine the value of a domain. Some of these criteria have to do with the spelling of the name, the level of ease at which people can remember it, the reputation it has had in the past and so on.
These names are considered premium because they are better than starting a site from scratch. You will be more likely to get more traffic and have a bit more respect because your domain name will signify that you are in control of your cyber world and you know how to get to the top of the crowded areas of the internet. You will not have a lengthy domain with misspelled words or excessive hyphens; you will have a simple, clear and direct domain that tells your clients exactly what you are about.
To get this much more, you will pay slightly more, sometimes a whole lot more than when making an original domain name. Whether or not this is worth it to you is your own decision and can be based on a multitude of factors.