For Extra Boost :

If you are an agency and your clients require the best engagement in the biggest subreddits, these are your accounts. They provide extra ranking boost and are also appropriate for posting in the biggest subreddits. These accounts inspire the most trust in redditors, moderators and Reddit's filter itself.

Dust :

Account without any verified email so far. This is an actual trophy.

Mature Account :

Every account with age 8 years or more. Reddit itself is 10 years old so these accounts are really valuable.

Natural Username :

These accounts have usernames that are real words or person names. Such accounts are rare and most of them were taken long time ago.