WhatsApp is adding end-to-end encryption to your cloud backups on both Android and iOS. While WhatsApp itself has been end-to-end encrypted by default for the past five years, until now if you chose to backup your chats to Google Drive (from the Android version of WhatsApp) or iCloud (if you're on iOS), those backups wouldn't be encrypted.
Now, however, you can turn on end-to-end encryption for your backups. The way WhatsApp owner Facebook describes this in its announcement, it seems like it won't be on by default but you'll have to actively choose to enable it by going to Settings > Chats > Chat Backup > End-to-end Encrypted Backup.
