It can be if the LLC elects S-corporation status, that is, files form 2553 and is accepted by the IRS. If it does not, it is taxed as a schedule C, sole proprietorship.
The IRS regulations allow the LLC to be taxed as either a partnership, a C-corp or as a disregarded entity. If no election is made, the LLC is disregarded.
No. A single member LLC is not taxed as an S-corp; it's taxed as a sole proprietorship. It's considered to be a disregarded entity for federal income tax purposes. A LLC, on the other hand, with more than one member can be taxed as a S-Corp or a Partnership.