1.种子轮（Seed round）
Seed funding is the first official equity funding stage. It typically represents the first official money that a business venture or enterprise raises. Some companies never extend beyond seed funding into Series A rounds or beyond.
创业者在创业初期需要资金的时候，往往由于产品还未成熟、商业模式尚未健全，多半无法获得创投公司的青睐而募到资金或进行A轮融资。因此，创业者在创业初期多半是向亲戚，朋友或小规模的基金等"天使投资人"募集小额资金。这个"pre-Series A"的阶段称为seed stage ("种子阶段")，而这个阶段所做的融资称为seed round financing ("种子轮融资").
一般来说，新创公司（Startup）的生命周期，不外乎经历以下阶段：从仅有一个想法的种子轮（Seed round）开始，而后有了「天使」（Angel）来投资。在过一段时间后，创投（Venture Capital；VC）、私募股权基金（Private Equity；PE）接连进场协助公司成长。
2.天使轮（Angel round）
An angel round is a type of funding for startups. It typically comes from wealthy individuals, known as angel investors, who invest their own money into a company.
Angel investors are usually people who have made their money in another industry and are looking to invest in a high-growth startup. They're often more interested in the potential return on their investment than in the day-to-day operations of the company.
Angel rounds can range from a few thousand dollars to several million, depending on the company's stage of development and the angel investors' level of interest.
天使轮，即天使投资，是指个人出资协助具有专门技术或独特概念而缺少自有资金的创业家进行创业，并承担创业中的高风险和享受创业成功后的高收益，或者说是自由投资者或非正式风险投资机构对原创项目构思或小型初创企业进行的一次性的前期投资。天使轮是比较特殊的一种风投融资方式。
当你的产品有了原型（prototype），也具备了初步的商业模式（是否可行，还尚待验证），甚至累积一些核心用户时，就会进入天使轮阶段。
此时期的投资人大多为天使投资人（Angel）、孵化器（Incubator）、加速器（Accelerator）、或是天使投资机构等等。
一般看来，天使投资人大多是累积了一定财富的企业家、成功创业者或是VC等。他们不仅可提供公司资金，有时还会为创业家带来人脉资源，是早期创业者的重要支柱。
3. A轮融资（A round）
The A round is normally the second stage of financing that a startup receives after the seed round and is also the first major funding round in the venture capital stage. In many cases, investors who provide A round financing typically receive convertible preferred stock.
当公司产品日益成熟，虽然还处于亏损阶段，但已有了完整的商业模式，在行业内也开始有一定的口碑，就会进入A轮融资。
从A轮开始，主要的投资人将由「Angel」转变为「创投」。创投，顾名思义就是创业投资（Venture Capital），指的是对新创公司进行有风险的投资。
4.B轮融资（B round）
Series B rounds are all about taking businesses to the next level, past the development stage. Investors help startups get there by expanding market reach. Companies that have gone through seed and Series A funding rounds have already developed substantial user bases and have proven to investors that they are prepared for success on a larger scale. Series B funding is used to grow the company so that it can meet these levels of demand.
当公司的商业模式已经几乎没任何问题；站稳现有市场后，计划推出新的产品线；或是要复制商业模式到海外市场，以加快规模化的脚步时，就会启动B轮融资。这时期的投资人以VC为主，而少数较早期的PE Fund也会加入。
5.C轮融资（C round）
Businesses that raise a Series C funding are already quite successful. These companies look for additional funding in order to help them develop new products, expand into new markets, or even to acquire other companies. In Series C rounds, investors inject capital into the meat of successful businesses, in an effort to receive more than double that amount back. Series C funding is focused on scaling the company, growing as quickly and as successfully as possible.
当公司已成为该领域的领先者，具一定的获利水平后，为了发展新型态业务，同时也为上市柜（Initial Public Offerings；IPO）做准备，便会发起C轮募资。此时期的投资人渐渐转向以PE Fund为主，而一些过去曾投资的VC也可能跟投。
拓展：
Pre-A轮、B+轮、B++轮、D轮、E轮，又是什么？
一般来说，融资募到C轮就差不多了。D轮指的是你把C轮的钱烧完了，但还没进入上市柜阶段；同理，E轮指的是你把D轮的钱烧完，但依旧还是没上市柜。
而大家常听到的Pre-A轮，指的是天使轮的钱花完了，但产品还不够成熟，尚未到A轮阶段，进退两难下，只好又募一个round，我们就称它为Pre-A轮。至于B+轮、B++轮都是相同意思，因为还没到下一round的水平，所以只好一直无限+++++。
来源：译问