Digital marketing is a broad term that encompasses all marketing efforts conducted through digital channels or electronic devices. It's about connecting with customers where they spend much of their time: online. The necessity of digital marketing arises from the increasingly digital nature of modern consumers' lives. Here are some key types of digital marketing:

1. Search Engine Optimization (SEO): This involves optimizing your website to rank higher in search engine results pages (SERPs) for relevant keywords. The goal is to increase organic (non-paid) traffic to your website.

2. Content Marketing: Content marketing involves creating and distributing valuable, relevant, and consistent content to attract and retain a clearly defined audience. This content can take various forms, including blog posts, articles, videos, infographics, and more.

3. Social Media Marketing:This involves promoting your brand and content on various social media platforms like Facebook, Twitter, Instagram, LinkedIn, etc. It includes both organic (unpaid) efforts such as posting content and engaging with followers, as well as paid advertising options offered by the platforms.

4. Email Marketing: Email marketing involves sending commercial messages to a group of people via email. It's used to promote products, services, events, and to nurture leads. Email marketing campaigns can be highly personalized and targeted.

5. Pay-Per-Click (PPC) Advertising: PPC advertising involves placing ads on search engines or other websites and paying a fee each time the ad is clicked. The most common form of PPC is Google Ads, where advertisers bid on keywords relevant to their target audience.

6. Affiliate Marketing: In affiliate marketing, businesses reward affiliates (partners) for each customer brought in through the affiliate's marketing efforts. Affiliates typically earn a commission for each sale or conversion they generate.

7. Influencer Marketing: This involves partnering with influential individuals on social media to promote your products or services. Influencers have dedicated followings and can help increase brand awareness and credibility.

8. Digital Display Advertising: This includes various forms of visual advertising that appear on websites, apps, or social media platforms. It can include banner ads, pop-up ads, interstitial ads, and more.

Each of these types of digital marketing has its own strengths and weaknesses, and businesses often use a combination of them to create a comprehensive digital marketing strategy tailored to their specific goals and target audience.