Ethernet port: this port is boxy in shape and looks like a slightly larger telephone jack. It is also called a "network port" "broadband connection" "LAN port" "RJ45 port" or "10/100" port.
* Higher speed ports are called "gigabit ethernet" and are referred to with the "1000" designation
Cable Modem / DSL modem: Your cable or DSL modem (most likely provided by your service provider) is the box that provides you internet access. Always make sure that your modem is not actually the problem.
Router: Some cable/DSL modems have built in routers, sometimes routers are a separate box. A router has multiple "ethernet ports" for connecting multiple computers. Always make sure that you are bypassing a router to check if the router is not the problem.
USB: The flat end (also called the "A" end) is the connection you will find on your Mac. This "flat end" plugs into a free USB port on your Mac
ISP: Means (Internet Service Provider) This is the company that provides you with internet service - such as AT&T, Verizon, Comcast, Charter, Hughes Net
DSL / PPOE: PPOE stands for Point To Point Protocol Over Ethernet - some DSL (if far away from service provider) and most satellite modems are configured with PPOE. Please realize that these settings need to be written down so you can configure your adapter to work with your ISP. If you need assistance with these settings ... typically your service provider can assist you via their customer service phone number.
DHCP/Cable Modem: DHCP stands for Dynamic Host Configuration Protocol - it is a type of network configuration used by devices (broadband modems, TIVO, Playstation, etc etc ) to obtain configuration information for operation in an internet network. This protocol reduces system administration workload, allowing devices to be added to the network with little or no manual intervention - hence the word dynamic.
Firewall: A firewall is a part of a computer or network with the purpose to block unauthorized inbound access while permitting outbound communication. It is also a device or set of devices configured to permit, deny, encrypt, decrypt or proxy all computer traffic between different networks (or domains) based upon a set of rules and other criteria. Typically a firewall is unnecessary on a Mac as other "rules and preferences" can be set within different programs like Safari, Mail, and even the Mac itself. If, as an average consumer you are worried about someone accessing your information - you should get a separate Mac for your financial or confidential matters - I would even recommend one of the original 1989 Mac SE/30 All In Ones. Firewalls can interfere greatly with just about all types of "network connections" - that is unless configured carefully by a knowledgeable network expert.