Customer retention refers to a company's ability to keep existing customers coming back. It's crucial for businesses as it's more lucrative than acquiring new customers, with customer acquisition costs being 5x more expensive than retaining an existing customer. Measuring customer retention involves tracking metrics such as customer retention rate, customer churn rate, repeat customer rate, and customer lifetime value. To improve customer retention, businesses can craft engaging onboarding flows, start membership programs, provide quality customer service, gather customer feedback, reengage inactive customers, personalize communications, infuse their business' personality into every interaction, and create referral programs. By doing so, companies can show their customers that they care about their experience and value their loyalty, leading to a positive customer journey and increased brand loyalty. Boosting customer retention and loyalty with tools like Twilio Flex is essential for businesses to thrive in today's competitive market.