If someone asked this question then there is no one answer for this. SharePoint is a very big system and has plenty of features. So, if we start talking about them then it will take weeks to cover all the features.
But in simple words "Microsoft SharePoint is an enterprise collaboration and content management platform which enables users to connect each other and share the information across an organization. Indirectly which solves the problems in an organization to
share the documents, security, business process, maintaining data etc. SharePoint 2010 has rich UI and plenty of features."
SharePoint core features:
1. Sites: You can create a web site in seconds from the UI. You can create how many sites you want according to your requirements and set the different permissions for each site. SharePoint 2010 comes with a rich UI and many improvements
to the HTLM as well. The team has replaced all the HTML Tables (in SharePoint 2007) with HTML Div tags (in SharePoint 2010). This makes a huge difference in rendering HTML on your browser, both in performance and time.
And the most important thing is the Ribbon (http://sharepoint-2010-world.blogspot.com/2011/02/ribbon-in-sharepoint-2010.html).
The Ribbon is a big revolution, and all the options are on the same page (multiple menus are combined into the Ribbon). The Ribbon properties change dynamically/automatically, depending on what context you are in. There is no need to leave the current page
to do something. Everything is on the page, and you can do the stuff that's needed. With this rich UI and ribbon support it is very easy to create and manage content in the site.
SharePoint 2010 sites can be browsable on any browser. The only limitation is it will not support IE6 (I believe no one is using IE6 still). So, we can call it Multi-Platform. This will be very good for developers and users who have their own impression
and habits regarding browser usage. You might prefer IE9 and Mozilla. Earlier versions of SharePoint don't work as well with browsers other than IE. So, that problem is resolved in this version.
SharePoint 2010 supports Cloud computing as well. So, you can host it in the general environment or in the cloud computing environment to give access to internet users. This is again a major feature included in SharePoint 2010.
2. Communities: It now includes more Social connections. You can connect to an employee [colleague] or users through user profiles, my sites (where each user has their own customizable SharePoint site), and people search. This way you are
connected with others and can share information very easily. Another thing in the communities section is "Informal Knowledge". This includes tagging, rating, and feedback features. For example, if many users are searching for a common document, then we could tag
that document with relative keywords. Now it will come up in the top search results. This way users get whatever they want very easily. Another option is rating. You can give a rating to a particular document or item.
3. Content: As we discussed in earlier sections now with SharePoint 2010, creating or managing content is very easy with the new rich UI and ribbon. This is very easy for admins to find the content in the site and to make changes. You may
feel that this is same as editing MS Office files like Word and PowerPoint in your browser. SharePoint 2010 manages huge and complex Metadata across site collections very easily.
4. Search: Search is a very big improvement in SharePoint 2010, compared to previous versions. The way the search has improved is unbelievable and gives the exact search results for what the user is looking for. There are many ways how the
team improved search. Here are the main ways:
5. Insights: This mainly covers the business process in an organization. The perfect implementation to this is workflows. SharePoint designer workflows are improved and many activities have been added to the 2007 designer activities. With
these we can solve many problems without writing custom code. And by writing custom code, you can create your own activities easily. Along with these there are improvements to the Excel Services and charts. In this version of SharePoint, the team integrated
Visio services. You can create a workflow in Visio and then import them to SharePoint directly. It is one of the fantastic features in this new version. The main advantage is someone who is good in Visio also has the option to do some stuff that will be useful
6. Composites: This concept comes from the Mash-Ups: Pulling information from different data sources and combining it single place. So, we can achieve this in 4 different ways:
So, finally, we can say SharePoint includes these abilities:
This article should help you understand the basics of what SharePoint 2010 is. Before we end this concept, I want to mention that SharePoint 2010 only supports 64-bit. (There is no 32-bit anymore.) So, all the infrastructure and the software (Windows Server
2008, Sql Server, etc.) should be 64-bit.