Difference between meta keys with _ and without _ [duplicate]

In wp_postmeta table I noticed that some of the keys are with ‘_’ (underscore) prefix and and some are without _

What is the major difference between these fields and how they can be used while theming ?

Is there any special use of fields with _ ?

Most of the plugins used this approach to create meta keys but there is not codex on wordpress regarding meta key naming, its not sure if there is any technical difference between these key names.

The underscore prefix are private, these meta fields will be hidden and will not be shown as custom fields in the post backend screens. Those meta fields without the underscore prefix are public fields and shows up as custom fields in the post screens