Email notifications are typically sent instantly, but an email digest combines most member emails into a daily summary.
Email Digests are a great way to keep updated on the content you follow without being inundated with notifications. Instead, you can choose to receive one daily email summarizing all of the activity you normally get individual, instant notifications of. This includes replies to discussions you follow, comments on your posts or My Page and new friend requests. An email digest will look similar to this sample:
Some emails like broadcast messages, personal messages and upload errors will continue to reach you immediately and are not included in your email digests. You can opt in to begin receiving digests for the content you follow and groups you belong to.