Orphan Nodes and Ways

You should try to understand the history of the objects (see object history, whodidit, OSMHV, attic, …). Were these objects not orphaned when they were created? Were they created as orphans? Was it just a single orphan object in a big changeset or were there many? Are the objects arranged in some special shape? Are there gps traces? Any recognizable from our aerial imagery?

Sometimes

• you can find newbies needing help,
• just the tags are missing and the creating user forgot to add them (mail the user),
• you can find other problems in the related changeset,
• (in year 2012, but maybe still today) that could be a surviving left-over from the redaction bot (license change) which may be an indicator that there is some feature missing (could be seen in aerial imagery sometimes).

At the end you may

• contact the creator/modifying user (see escada's answer) and
• add relevant tags, delete the object or leave a fixme tag with some already collected info for fellow mappers who might know the location better than you.

It would not be beneficial to just delete these objects. That could remove a valuable hint for other mappers that there is something (of importance) missing.

If you are still quite new to OSM then this might not be the right task to start with.

Contact the mapper that created them via a changeset comment or private message in (of course) a friendly way. Wait a couple of days to give them the time to react. This way you give them the possibility to learn. In case they do not react, or when you see they have not been contributing in a long time, you can remove them yourself.