Every contact and company in HubSpot has a lifecycle stage property. The default stages run from subscriber through lead, marketing qualified lead (MQL), sales qualified lead (SQL) and opportunity to customer, with evangelist and other at the end. HubSpot records the date each record entered each stage, which is what funnel and conversion reports are built on. Depending on your subscription and portal age, you may be able to rename or adjust the stages in your lifecycle stage settings.
Lifecycle stage is meant to move one way. Most HubSpot automation, including workflows and form settings, will only move a record to a later stage, not an earlier one. To move a record backward, you first clear the property and then set the earlier value. This protects funnel history, but it also means a wrong stage set early by an import or integration will stick until someone fixes it on purpose.
The property matters because so much depends on it. Segments (lists in older portals), lead scoring handoffs, nurture workflows and conversion reports all filter on lifecycle stage. If stages are blank or set inconsistently, contacts miss the right emails, sales receives the wrong leads, and the MQL to SQL conversion rate in your reports stops meaning anything.
Teams that use it well write down a short definition for each stage, including who or what is allowed to set it. A common pattern: marketing automation sets lead and MQL, sales sets SQL, and deal creation or a closed won deal moves contacts and companies to opportunity and customer. Everything else is set by workflow, not by hand.