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Plain-English definitions
Tax glossary.
Tax forms come with their own vocabulary, and half the confusion in a first filing is just not knowing what a term means. This glossary defines, in plain English, every term used elsewhere on this site.
Who this is for.
First-time S-Corp owners and first-time 1040 filers get the most use out of this page — the people encountering "apportionment" or "reasonable compensation" for the first time in their lives, not tax professionals who already know the vocabulary. If a term feels obvious to you, it's probably not written for you specifically.
Why we built this.
Terms like "reasonable compensation," "apportionment," or "Schedule E" show up throughout our service pages and guides. Rather than re-explain each one inline every time, we define it once here and link to it — so pages stay readable and the definition stays consistent.
How entries are organized.
Entries are grouped by filing type — S-Corp terms, individual-return terms, and general tax-prep terms like EFIN, PTIN, and ERO that apply to any client. Each entry is a short, one- or two-sentence definition, not a full article; if a term needs more depth, it links out to the relevant guide.
When a term needs more than a definition.
A glossary entry tells you what a term means. It doesn't tell you whether it applies to your specific return — reasonable compensation rules, for instance, depend on your industry and shareholder role. For that, the Tax Guides go deeper, or a quick call with a preparer settles it directly.
A few terms clients ask about most.
ERO (Electronic Return Originator): the firm authorized to transmit your e-filed return to the IRS. EFIN: the number the IRS assigns that ERO. PTIN: the number assigned to an individual preparer, separate from the firm's EFIN. K-1: the form each S-Corp shareholder receives showing their share of the company's income for the year.
Filing now · FY 2026
Pick your form.
Pick your form.
We'll take it from there.
Two forms, two deadlines, one workflow. Tell us which return you're filing and we'll send the SmartVault link and document checklist within the hour.
S-Corp · Form 1120S
Mar 15
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Individual · Form 1040
Apr 15
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