AD Connect

Microsoft Entra Connect is an on-premises Microsoft application designed to meet and accomplish your hybrid identity goals.
Microsoft Entra Cloud Sync is the future of synchronization for Microsoft. It replaces Microsoft Entra Connect.
Microsoft Entra Connect features

Password hash synchronization

Pass-through authentication

Federation integration

Synchronization

Health Monitoring

Microsoft Entra Cloud Sync is a new offering from Microsoft designed to meet and accomplish your hybrid identity goals for synchronization of users, groups, and contacts to Microsoft Entra ID.
Comparison between Microsoft Entra Connect and cloud sync

Microsoft Entra Connect Sync synchronize changes occurring in your on-premises directory using a scheduler.
There are two scheduler processes, one for password sync and another for object/attribute sync and maintenance tasks
The new default synchronization frequency is 30 minutes.
The scheduler is responsible for two tasks:

Synchronization cycle. The process to import, sync, and export changes.
Maintenance tasks. Renew keys and certificates for Password reset and Device Registration Service (DRS). Purge old entries in the operations log.

To see your current configuration settings

Get-ADSyncScheduler

Related - Youtube video

Azure AD Connect - Complete Series

Office365Concepts, 14 videos

01 ~ 00:09:24 ~ What is Azure AD Connect | Benefits of Azure AD Connect | What is Hybrid Identity model

02 ~ 00:08:14 ~ Azure AD Connect Architecture: Exploring the Sync Engine, Connector Space, and Metaverse Components

03 ~ 00:03:37 ~ Azure AD Connect prerequisites | Azure Active Directory and on-premise Active Directory prerequisite

04 ~ 00:04:06 ~ Azure AD Connect service accounts | Service accounts used by AAD Connect to sync users to Azure AD

05 ~ 00:19:54 ~ Azure AD Connect Installation and Configuration: Express and Custom Settings

06 ~ 00:18:20 ~ Azure AD Connect Filtering |Configure Group based, Domain based, OU based, Attribute based filtering

07 ~ 00:16:44 ~ Syncing Users in Azure AD Connect: Master the Art of Seamless User & Group Integration

08 ~ 00:08:52 ~ Azure AD Connect Sync Scheduler | What is Sync Scheduler in AAD Connect | Customize Sync Scheduler

09 ~ 00:08:11 ~ Azure AD Connect Declarative Provisioning | Sync Rules Architecture | Components of Sync Rules

10 ~ 00:17:29 ~ Synchronization Rules Editor in Azure AD Connect | Create custom synchronization rules

11 ~ 00:14:01 ~ What is Password Hash Synchronization | How Password Hash Sync works | What is Password Hash

12 ~ 00:06:26 ~ What is Pass through Authentication | how pass through authentication works

13 ~ 00:16:00 ~ What is Soft Match and Hard Match in Azure AD Connect | How to Soft Match and Hard Match

14 ~ 00:08:40 ~ Azure AD Connect Staging Mode: Convert Active Mode to Staging Mode