My answer here is more about the actual engineering to make an antenna operate efficiently across a wide band of frequencies. I am an amateur (Ham) radio operator and I have been designing and using antennas of various kinds for almost 60 years. So, this is about my antennas and how they are made to work efficiently for both receive and transmit.
As an example, one of my current antennas (I have four antennas in use right now) is an 80-meter dipole that is about 136 feet in length and an average of 55 feet in the air above ground. It is center fed with "ladder-line" transmission line to achieve low-loss. It is copper wire (actually, ordinary #12 house wire).
It is named 80-meter for the principle frequency band of use. This 80-meter band (sometimes the upper end is referred to 75-meter band) is designed for 3.5 MHz to 4.0 MHz operation. However, I use this very same antenna with the 40 meter band (7.0 to 7.3 MHz) and the 30 meter band (10.1 to 10.15 MHz). Technically, it can handle not just thousands but an continuum of frequencies. [Note: the total number of "frequencies" simultaneously used by a given band (e.g. 80) meter band is dependent on the band-with of the signal versus the band with of the antenna. I operate CW mostly (Morse Code) and bandwidth is under 250 Hz. A SSB signal though is roughly 3.0 KHz.]
Antennas can be operated as resonant antennas and also used for non-resonant operation. All AM and FM or even SW receiving-only antennas are non-resonant. Resonance is something that happens at specific frequencies. For example, my 80-meter dipole antenna was designed to be resonant at 3.505 MHz. However, the resonance point of an antenna is affected by a lot of different things such as height over ground, conductivity of ground, nearby conductive structures (metal, trees, etc.). So, often when building an antenna like an 80-meter dipole you purposely make it longer than necessary and then measure the impedance at the desired frequency and then cut or trim the antenna and re-measure until you are close enough. You measure impedance at the antenna feed point because you want the reactive portion ($X$) of the complex impedance of $R+j X$ to be zero ideally.
Physically measuring the antenna feed point impedance is most often not easily done. In my case, it is 55 feet up in the air. So, I measure the impedance on the other end of the transmission line which is physically accessible and I take into account the impedance transforming affect of the transmission line itself. This is a simple calculation (or, you can be like old-timers and use a Smith Chart).
So, there is one resonant frequency to the antenna but I use it for a wide range of frequencies. The result of operating off of the antenna resonant frequency (below or above) means that the impedance is different and often it is a very bad mismatch to the rest of the equipment. This mismatch in impedance means that losses in the system (mostly in the transmission line) are increased and usually to such amounts that it is worthless as an antenna.
To fix this problem, the antenna is coupled via an LC circuit that is tunable. This tunable circuit is often referred to as an "antenna tuner" but it comes by a variety of names. For example, many of the old SWL receivers included a variable capacitor (sometimes inductor) called "Antenna Trimmer" and by turning this inductor knob you could strengthen signals by getting a closer match in the impedance to the antenna circuit. My antenna tuner is more sophisticated and automatic (I don't need to turn any knobs) with built-in processors (Elecraft KAT500). However, mine is designed to handle a transmitted signal as well as a received signal.
For receiving, antennas can be mismatched and the only bad outcome is a more poor signal or maybe the signal is not even above the noise level as a result. But, for transmitting, a mismatch in the impedance results in standing waves on the transmission line which can result in great losses but also in high-voltages where the transmission line connected to the transceiver. With solid-state equipment, these high-voltages can damage the equipment so they are to be avoided. Indeed, the modern solid-state transceiver has built in circuitry to continuously measure and automatically back off on transmitted power (even to the point of shutting down transmission) until the danger is alleviated.
The key measure is called the Standing Wave Ratio and ideally you want this ratio to be as close to $1:1$ as possible. On my 80-meter antenna, the resonant point on the antenna still has a high-SWR because the resonant resistance is near 70 ohms but I am feeding that antenna with 450-ohm transmission line (ladder-line) and this transforms the impedance I see at the transceiver is something quite different from the resonant antenna feed point resulting in a mismatch SWR of about $5.6:1$ and this should be less than $2:1$ as above $2:1$ the transmitter cuts back power more and more until at $3:1$ the transmit function is switched off.
Making antennas work efficiently for both receive and transmit on multiple frequencies and even multiple bands of frequencies is a big part of the hobby of ham radio. There is probably more lore and written material, both correct and incorrect, on ham radio antennas than any other part of the hobby. HF radio antennas is not plug-and-play, lots of engineering design and other technology comes to play to make it work.