VoIP, or Voice over Internet Protocol, is a technology that allows voice communications and multimedia sessions to be delivered over the internet or other IP-based networks. Instead of using traditional analog phone lines, VoIP converts voice data into digital packets and transmits them over the internet.

Here are some key points about VoIP:

1. Cost-Effective: VoIP services often offer cheaper long-distance and international calling rates compared to traditional phone services. Additionally, many VoIP services offer flat-rate plans allowing unlimited calls to certain areas, further reducing costs for businesses and individuals.
2. Flexibility: VoIP users can make and receive calls using a variety of devices, including dedicated VoIP phones, computers with headsets, or even mobile devices with VoIP apps.
3. Features: In addition to basic calling features, many VoIP services offer a suite of advanced functionalities, such as voicemail-to-email, video conferencing, call forwarding, and more.
4. Quality: While early VoIP services were sometimes criticized for subpar call quality, advances in technology have greatly improved VoIP call clarity. Nowadays, with a good internet connection, VoIP calls can be as clear as, or even clearer than, traditional phone calls.
5. Portability: With VoIP, users can move their VoIP device or phone to a different broadband network connection, and their phone number and configurations typically move with them. This is especially beneficial for businesses or individuals who travel or relocate frequently.
6. Reliance on Internet: One downside is that VoIP requires a stable and high-speed internet connection. If the internet goes down or if there's significant latency or packet loss, it can affect call quality or availability.

Popular services like Skype, Zoom, and WhatsApp use VoIP technology to enable voice and video calls over the internet.

Overall, the adoption of VoIP has been growing rapidly due to its cost savings, flexibility, and array of features. Many businesses and consumers have either supplemented or entirely replaced their traditional phone lines with VoIP.