Unless the conference is longer than 90 days, you both need a Schengen short-stay visa, which is also known as a Type C visa. The Schengen area does not subdivide the type C visa into different classes, but the application form does ask you to specify the main purpose of your visit using one of several choices:
- Visiting family or friends
- Official visit
- Medical reasons
- Airport transit
- Other (please specify)
Your wife could either choose "tourism" or "other"; in the latter case she would add something along the lines of "accompany S M Ferdous to conference."
You and your wife will need to submit separate applications, but you should each refer to the other's application in your cover letter. The cover letter is required; you can see the list of other required documents by visiting the visitor's visa page for applicants in the US and following the "Document Checklist" link in the second section of the page.