accdb: That's the file extention for files created by Access (2007 or newer). The good thing about accdbs is that they are handy to work with and you can move them around fairly easily.
The bad thing about accdbs is that the wrong person can move them around easily, and even remove them from your premises. That's one of the main reasons we usually recommend SQL Server for your databases.
action query: Databases use queries to select or change or delete data in the database in several ways. Queries are like messengers scrambling back and forth between the front desk and the back room; their job is to carry information or perform tasks on behalf of the customer at the front desk. One type, action queries, handles inserting, updating, or deleting data in tables.
End users seldom see, or even know about action queries; they run behind the scenes in code we create for your database.
aggregate query: Some functions in a database require creation of totals, sums, maximums, averages, and so on. Agregate queries handle that job. You'll see their results in a lot of reports. Some people call them totals queries. Several types of queries can be aggregate queries; including select, append and make table queries.
alias: An alias is  user-friendly name for something in a database. Many expressions and object names in a database have long or odd-looking names. We often alias them so we have a more user-friendly name to work with or to show to your end users.
append query: When we want to insert more than one row of data into a table, it's more efficient to use an append query to select and insert them all at once. Say, for example, all of the product detail lines on an invoice for a grocery store might be appended to a shipping record for the shipment to that store.
application fields: Sometimes the user adds data directly to the database (e.g. the name and address of a customer), but sometimes data can be automatically added by the system without users having to bother (e.g. the date and time the customer's information was added). Those are application fields.
archive table: How quickly you can get information out of your database depends, in part, on how big it gets. Some systems include a function where records that are no longer needed for the day-to-day operation of an application are moved to an archive table. It's sort of like renting a storage unit for the stuff you don't use, but can't throw away.
argument(s): Programmer's mumbo-jumbo. Seriously, when we write re-usable code for your application to save time and resources, we usually need arguments to hand the correct values to that code to use in processing.
attachment data: Both Access and SQL Server have special fields that can hold various forms of data-- or even files. We call that attachment data. It could be an image, a PDF, or even a Word doc.
attributes: When storing information about many instances of a single thing, like a customer, you need to identify characteristics or qualitities to differentiate one from another. We call that attributes. First and Last Names are a good example of two customer attributes in a retail clothing store database.
autoindex: Access tries to be helpful by creating indexes for some fields which it thinks should be indexed. By default that includes fields whose names have suffixes like ID, num, code, and key. Sometimes Access guesses wrong, so you should let your developers worry about all that.
autojoin: Access knows that some tables are, or should be related. SalesPersons and Orders, for example. Therefore, Access automatically joins those tables together in the query designer for you. By default the option is enabled. Since we don't expect end users to write many queries, you may never see it in action, but if you do, it's a handy feature.