A nerd is a person who is highly enthusiastic and knowledgeable about a particular subject, especially one of specialist or niche interest, and engages in or discusses a technical field obsessively or with great attention to detail.
However, a key difference is that nerds are "achiever" focused on knowledge and skill acquisition and are intellectual enthusiasts concentrate on mastering a topic, sometimes to the exclusion of social activities; While geeks are enthusiastic fans of a specific subject, they often collect related items and share their passion in groups and are more like a "collector" of facts and memorabilia.