Inbound marketing, a term coined by Brian Halligan, is employment of ‘pull’ marketing rather than ‘push’ marketing strategies.
A pull strategy involves motivating customers to seek out your brand in an active process.
“Getting the customer to come to you” (Marketing made simple)
Pull strategies are designed to brand loyalty and keep customers coming back to you. Content Marketing, for example, is a pull strategy.
Inbound marketing is specifically about creating content, then via SEO techniques and social media helping customers find your content. If the content is any good, your leads will keep coming back until you can convert them.
Here’s a good infographic from Hubspot.