Tab syncing is a feature that Google has been working into Chrome since it first appeared in the Beta and Canary builds back in early April. Today's Stable Google Chrome release (version 19) marks the first time all users have been given access to the feature.
Tab syncing allows users who have signed into Chrome to have all their open tabs seamlessly shared between all their instances of Google's browser. This includes all their computers and any Android devices running Ice Cream Sandwich that have Chrome for Android Beta installed.
While the updated version of Chrome will be available to all users immediately, the tab syncing functionality will roll out more gradually over the course of the next few weeks. This isn't unusual to the approach Google has taken with their rollouts of other features in the past.
Signing in to Chrome and enabling sync also brings a variety of other benefits. Various information including the user's history, extensions, themes, apps, and settings are all carried between any Chrome instances sharing your sign-in information.
Source: Chrome Blog