'What is Slack?' Everything you need to know about the professional messaging program.

• Slack is a messaging program designed for use in the workplace.
• It's available for desktop and mobile and can be used through the Slack website on a web browser.
• There's a free version, but if you want the full version, it's at least $6.67 a month per person.

If you work for a large enough company, or for an organization with any remote employees or freelancers, chances are that at some point you're going to be asked to join Slack.

What started out as an internal chatting program for one company has grown into the primary communication and workflow platform for companies, nonprofits, and other organizations around the world.

Here's what you need to know about Slack, which is available for Mac and PC and iPhone and Android devices.

What you need to know about Slack

Think of Slack as a chatroom shared among all the members of an organization.

Your organization is known as a "workspace" and is divided into "channels," which are separate group chats with their own members and topics.

In these channels, you can send messages, images, internet links, videos, and more. They're designed to make communication between employees seamless, and replace many of the functions that email once dominated.

There are also direct messages, which let you chat with one or several people privately without anyone else being able to join.

Slack is also built to sync with the apps that your company uses every day, like Google Calendar and Google Drive.

Your administrator can install apps in Slack, which let you use them without ever leaving the chat you're in.

Administrators can also set how long chat messages are kept for. By default, messages are kept indefinitely, which means you can use the search function to find messages from any time. But many organizations choose to delete messages after a set amount of time.

Slack apps are available for Windows and Mac computers and Apple and Android mobile devices. You can access the same functionalities through Slack's website in a desktop web browser.

How the different tiers of Slack compare

The free version of Slack allows you to search through the most recent 10,000 messages and add a limited number of people to your workspace.

Paid versions of Slack, which are billed based on how many members your workspace has, give you unlimited search, and the ability to add more apps and members than the free plan.

The Standard paid plan costs $6.67 a month per active user, while the Plus version goes for $12.50 a month per active user. You'll need to contact Slack directly to get a quote for the ultimate "Enterprise Grid" payment plan. There are discounts available for nonprofits and educators.

Other bonuses in the paid plans include heightened account security, encrypted messaging, data loss prevention, group calling, and more.

For more information on what each individual Slack plan offers, check out the website.

Related coverage from Tech Reference:

• There's a super-easy way to see who sends the most Slacks at your company - here's how to do it

• How to search in Slack for relevant messages and files on your computer or mobile device

• How to create a Slack channel on a computer or mobile device

• How to rename a Slack channel in 2 ways and give every group in your office a distinctive name

• How to delete Slack messages that you've sent, and what to do if you can't delete them