Spread means how many repository families (e.g. all Debian versions as well as Ubuntu and other derivatives make a single family) contain this package.
newest#repos - newest known version. The number shows how many repository families have this version.
devel - newest known devel (or unstable) version. There may be both devel and newest versions for a given package.
unique - package is only present in a single repository family, there are no other sources to compare it against, so although it's the latest version known to repology, is not really reliable.
outdated - outdated version which requires updating.
legacy - outdated version when a newer version is present. This is assumed to be legacy version preserved for e.g. compatibility.
rolling - package is fetched from always latest snapshot or VCS master/trunk, so it is always latest and is not a subject for comparison.
noscheme - the project does not have official versioning scheme, so versions used in repositories which are basically random.
incorrect - version is known to be incorrect (e.g. version not officially released yet, or lacking alpha/beta/rc qualifier).
untrusted - this source is known to likely supply incorrect versions, so is ignored proactively.
ignored - version is ignored and excluded from comparison for some other reason (e.g. snapshots).
vulnerable▲ - version is potentially vulnerable as there are related CVEs.