Redirect 301

301 redirect is a permanent redirection. It informs search engines that the URL they’re trying to access has been changed permanently.
When you delete pages or change URLs, they don’t disappear, and in order to avoid from receiving 404 errors ,it is best practice to use a 301 redirect.
301 redirects will redirect users and search engines from these old URLs to new active pages that you specify. This also ensures avoid confusing users, and to pass on search results authority from these old pages to the ones. And also in cases that people who have linked to or bookmarked the old address will automatically get to the new one, and search engines can update their index.

Additional Terms:

Rich Snippets
Ecommerce
Social Media
Yandex
Search Engine Reputation Management (SERM)/ Online reputation management (ORM)
Google Partner/Premier Google Partner
Responsive Website
Mobile-Friendly website
Google maps
Hashtag
Call To Action
Bounce Rate/Abandonment Rate
Mobile Marketing
Content Marketing 
Marketing Automation / Programmatic
Website Traffic/ Traffic Analysis
Geo Targeting
Quality Score
Lead Generation
A/B Testing
B2C Digital Marketing
B2B Digital Marketing
Doorway page
Dead/ Broken link
Wikipedia
Robots.txt
Internal Link
Outbound Link
Inbound Link
Heading tags
Google Trends
Google Sitelinks
Google Keyword Planner
CTR (click-through rate)
CPC (Cost Paid per Click)
404 Not Found
Redirect 302
200 OK Code
Alt attribute/ Alt tags
Nofollow link
Search engine algorithm
White hat search engine optimisation
Black hat search engine optimisation
White hat SEO
Google’s Penguin Update
WordPress
Usability
Organic Search Results
Link Building
Landing Page
Google Dance
Indexing
Email Lists
Duplicate Content
Domain
Canonical URL
Blog
Banners
Algorithm
Accessibility
Conversion Rate
Satellite Websites
Bid
Joomla
Google’s Knowledge Graph
Drupal
Link Exchange
Long tail
Google Webmaster Tools
Lead
Magento
Keywords
Mini Site
Search Engine
CMS
Site Map
Player Embed
Bread Crumbs
Google Panda Update
YouTube Channel
Contextual Advertising
Open Source
Google’s Search Engine Robot
Meta Tags
Affiliate Program
CPA - Cost Per Action
CPL - Cost Per Lead
Friendly URL
GDN – Google Display Network
Page Rank
Remarketing
ROI – Return on Investment
RSS (Really Simple Syndication)
SEM-Search Engine Marketing
XML–Extensible Markup Language