The 3dB frequency of a filter is defined as when the voltage gain $V_{out}/V_{in} = 1/\sqrt(2)$. There's a slight rounding difference when converting to decibels as $20\log(\sqrt{2}) = -3.012 \mathrm{dB}$, but that would get very tedious to write.

A Breadboard is, in general, a surface designed to have circuits built on it.

The name originates from around the 1920s, when amateur radio enthusiasts would literally use a wooden cutting board meant for bread as a platform to build circuits on.

Nowadays it generally describes specialty prototyping boards that have rows of metal strips with spring-leaf clips below a plastic housing with evenly spaced holes.

A Bus is something used to transmit signals or powering voltages over long distances. In this class we'll use the later definition more frequently, as often we'll want to connect multiple components to the same voltage (commonly +5V or 0V) without turning everything into a mess of wires.

The Cutoff Frequency of a filter is the threshold used to define when when the output voltage changes significantly from the input. Frequencies above/below (depending on filter type) are significantly attenuated and thus 'cut off' from the signal.

The meaning of 'decibel' in electronics is a bit convoluted. It was originally defined in terms of power transfer, with an attenuation of 10 decibels corresponding to 1/10th of the power transferred, 20 dB to 1/100th, and so on.. When discussing signals, we're trying to characterize voltage changes. Since the power dissipated by an element is $P = VI$ and for an ohmic element $I = V/R$, then $P = V^2/R$. This means a change in voltage by a factor of $\sqrt{2}$ will correspondingly change the power by a factor of 2. The end effect is that a change of 20 decibels corresponds to 1/10th the original voltage, 20 dB to 1/100th, etc.

When a circuit has both an input and output voltage denoted, the ratio of the output to the input amplitudes is called the 'gain'. Gain can be denoted for dc voltages or as a function of frequency. A circuit with only passive components (resistors, inductors, and capacitors) has a maximum gain of 1, but when using active components (e.g. transistors and op-amps) it is possible to have positive gain (i.e. amplification). Gain is a very useful concept later when it comes to processing signals using multiple connected circuits.

A point in a circuit that is regarded as 0V when making measurements relative to it. In some instances such as battery powered circuits this can be arbitrary, but many times it is tied to what is considered 0V in a device's (and therefore building's) wiring. In electronics jargon, Earth is often used to denote what is called “ground” in electrostatics, i.e. a connection to a sufficiently large conductive body that can receive or emit any quantity of electrons.

An Integrated Circuit (IC) is a device that has a complete circuit made out of components etched in silicon that perform a specific function together. They're much smaller than what you could build out of individual parts, and will save a huge amount of time over building everything from scratch.

You could build a basic computer processor out of about 1000 transistors yourself , but you could instead buy something orders of magnitude better in every way for about $4.

The voltage/time plot shown on an oscilloscope. The 'trace' part of the name comes from old analog oscilloscopes, where an electron beam was used in the display. The oscilloscope deflected the beam as a function of the input voltage, causing it to trace out (draw out) the image.