DNS lookup, or Domain Name System lookup, is the process of translating a human-readable domain name into an IP address. In simpler terms, it's like looking up a contact in your phone by their name to find their phone number.

Here's how it works with an example:

Let's say you want to visit a website, like "www.example.com", in your web browser. Your computer first needs to find out the IP address associated with that domain name so it can connect to the website's server.

1. Request: You type "www.example.com" into your web browser and hit enter.

2. DNS Query: Your computer sends a DNS query to a DNS server, usually provided by your Internet Service Provider (ISP) or configured in your network settings.

3. DNS Lookup: The DNS server receives the query and checks its records for the IP address associated with "www.example.com".

4. Response: If the DNS server has the IP address cached (stored in its memory), it immediately returns the IP address to your computer. If not, it queries other DNS servers in the hierarchy until it finds the IP address and returns it.

5. Connection: Armed with the IP address, your computer can now establish a connection to the server hosting "www.example.com" and retrieve the web page.

The main uses of DNS lookup include:

1. Website Access: DNS lookup is essential for accessing websites using domain names rather than IP addresses. It makes the internet more user-friendly by allowing people to remember and use domain names instead of long strings of numbers.

2. Email Delivery: DNS lookup is also used for email delivery. When you send an email, your email client uses DNS to find the IP address of the recipient's mail server so it can deliver the message.

3. Load Balancing: Websites often use multiple servers to handle incoming traffic. DNS lookup can be used to distribute this traffic among different servers based on factors like server load or geographic location.

4. Content Delivery Networks (CDNs): CDNs use DNS lookup to determine the closest server to a user, reducing latency and speeding up the delivery of content such as images, videos, and web pages.

In essence, DNS lookup is a fundamental process that underpins much of how we interact with the internet, enabling seamless communication and access to online resources.