Short definition
CRM is software that stores every lead, customer, and interaction in one place so a service business can follow up faster, sell more, and stop losing deals to a forgotten inbox.
In depth
A CRM (Customer Relationship Management system) is the central database your sales and service team works out of. It captures form fills, phone calls, texts, and emails, attaches them to a contact record, and moves that contact through a pipeline of stages from new lead to closed-won. Modern CRMs add automation: auto-text every new lead in 60 seconds, schedule follow-up tasks, send review requests after a job, and report on which marketing source actually produced revenue. For service businesses, the CRM is the difference between a hot lead getting a quote in two minutes and the same lead going cold in someone's inbox over the weekend.
Example
A roofing contractor uses GoHighLevel as their CRM. When a homeowner submits a quote form, the CRM auto-texts them, books an estimate on the calendar, and reminds the rep 30 minutes before the appointment.