Customer Success (CS) can be defined as the role/department that owns the relationship between the company and the customer post-sales. The CS department is responsible for making the customer successful and happy with your product. CS is the natural evolution of the old tried and true "customer service" department, with a bigger focus on -and commitment to- the customer's success rather than simply "serving" the customer. CS is the team that should have the best understanding of customer "health" and attitude.
The CS Team is usually involved in (but not limited to):
- Product Onboarding (including implementation and training)
- Ongoing Support
- Communication and Check-ins with Customers
- Customer Retention and Churn Reduction
CS has an interesting perspective in an organization. Since they generally have the most interaction with a customer, they have a unique vantage point into what works, and more importantly, what doesn't work within the product or services offered by the organization. It's the CS team's job to champion the customer's needs, wants, and must-haves to the rest of the organization.
In a well oiled organization, customer success should be routinely checking in with product teams to tweak the products based on customer feedback. The product teams would then take the feedback from the CS team, and incorporate changes into the product. This cycle should naturally be happening constantly as you approach product market fit, and continually as the market changes and adapts as markets are wont to do. This iterative development process with an eye toward data and customer feedback is the backbone of growth hacking.
Companies like Automattic and Zappos put Customer Success/Happiness before almost all other functions; Zappos goes as far as to be dogmatic about providing the best customer service in the world, and their entire company culture is built around those precepts.